One DS9 speculative script and multiple unused stories were devised by Christopher L. Bennett. He recalled, "My DS9 spec script actually got me a pitch invitation. I went out to L.A. and pitched to Robert Hewitt Wolfe; he didn’t take any of my pitches, but his comments about them drove home the importance of focusing on character, a lesson that’s been very helpful to me." (Voyages of Imagination, p. 146)
Three DS9 story ideas were conceived by Armin Shimerman, Eric A. Stillwell and David R. George III. Recalled Shimerman, "David George, partnered with Eric Stilwell, asked if I would join them to pitch episode ideas for Deep Space Nine. We worked for several months honing our plot points and eventually had our shot with writer/producer René Echevarria. Unfortunately, No sale." (Voyages of Imagination, p. 245)
Similarly, three story pitches were suggested by Gary Holland at a pitch session with Ira Steven Behr, Robert Hewitt Wolfe and Peter Allan Fields, toward the end of DS9 Season 2. Although one of these ended up as the genesis of DS9: "The Collaborator", the other two ideas were quickly dismissed by Behr, Fields and Wolfe. (Star Trek: Deep Space Nine Companion, p. 147)
One undeveloped character concept was that, in the third season episode "Second Skin", Robert Hewitt Wolfe – who wrote the installment – wanted to establish that Kira Nerys basically wasn't, in fact, Bajoran. "Originally," reported René Echevarria, "Robert wanted to say that Kira was Cardassian, that the arc of the show was that the real [Bajoran] Kira died, but she [Kira's Cardassian counterpart] is essentially Kira now and it doesn't really matter." Rick Berman and Michael Piller objected to this proposal. "I think Rick and Mike [...] thought that it was too weird, too alien a notion for the audience to really hold on to a character they had invested themselves in [....] They were probably right in that decision." Echevarria also observed that the abandoned concept was "very similar to when we wanted to kill Will Riker and keep" his transporter duplicate, Thomas Riker, in TNG: "Second Chances". (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 85)
Cardassian O'Brien storyEdit
A plot idea Robert Hewitt Wolfe thought up for DS9 focused on Miles O'Brien and stemmed from an undeveloped TNG story. "I kept thinking about a way to do that as a DS9 episode," he remembered, "and for a long time thought it would be cool if O'Brien was a Cardassian who had been replaced when serving on the Rutledge." (Cinefantastique, Vol. 27, No. 4/5, p. 95) In fact, Wolfe imagined O'Brien having been replaced during the Setlik III massacre. (Star Trek: Deep Space Nine Companion, p. 177) This would have made O'Brien conceptually very similar to Raymond Boone, from DS9: "Tribunal". Wolfe explained, "The replacement [in O'Brien's case] was a deep-cover agent who'd been given O'Brien's memories [and didn't know he was Cardassian]." (Star Trek: Deep Space Nine Companion, p. 177) A problem of logic faced Wolfe, though, as he couldn't understand why, if O'Brien was actually a Cardassian, his daughter, Molly O'Brien, looked Human. Wolfe rewrote the episode as "Second Skin", replacing Miles O'Brien with Kira Nerys. (Cinefantastique, Vol. 27, No. 4/5, p. 95)
A story inspired by magician Jeff McBride was devised for the series by Christopher Teague, with the intention of enabling McBride to appear in the episode. (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 84) The plot concept was pitched to DS9 by Teague and bought from him. Ronald D. Moore later recalled that the story regarded a "circus coming to Deep Space 9, and this magician was in it." René Echevarria added, "It was an Odo show, about Odo's dreams, or a figure that he was chasing." (Star Trek: Deep Space Nine Companion, pp. 174-175) This figure was a mysterious, masked man, inspired by masks used by McBride during his show. (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 84) The idea of bringing a visiting circus onto DS9 didn't appeal to the writers. "We thought, 'Well, we're not gonna to do that,'" related Moore. (Star Trek: Deep Space Nine Companion, p. 175) Nonetheless, the DS9 writing staff struggled with the story concept, eventually rewriting it as the episode "Equilibrium". (Cinefantastique, Vol. 27, No. 4/5, p. 95)
Cold and Distant StarsEdit
A story imagined by Robert Hewitt Wolfe involved Benjamin Sisko waking up on a beach in 1995 Santa Monica, disheveled and disoriented. He was aware he was a Starfleet commander, though everyone around him believed he was mad. (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 89) Related Wolfe, "I wanted Sisko to be saying, 'I'm the captain of a starbase in the year twenty-three-whatever, and I don't belong here.' And everybody's telling him, 'You're a homeless schizophrenic, take your Thorazine.'" Wolfe wrote the concept into a script called "Cold and Distant Stars". The title related to Sisko, as a homeless man, looking up at the sky in the knowledge that was where he belonged.
There were problems with the story. "That never quite worked," Robert Wolfe admitted. (Star Trek: Deep Space Nine Companion, p. 196) He further critiqued, "The problem with my concept is that Brannon [Braga] went and did it with Riker in an insane asylum [in TNG's "Frame of Mind"]." (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 89) Ira Steven Behr agreed, "It just didn't work for me." (Star Trek: Deep Space Nine Companion, p. 196) However, Wolfe managed to sell Behr the idea – which Wolfe later referred to as "snake oil" – in DS9 Season 2. Reflected Wolfe, "I sold him the idea that Sisko would wake up on Santa Monica beach. He would say, 'I am a starship captain,' and the locals would say, 'Yeah, right.'" (Cinefantastique, Vol. 27, No. 4/5, p. 92) The story was rewritten as third season two-parter "Past Tense, Part I" and "Past Tense, Part II". (Star Trek: Deep Space Nine Companion, p. 196; Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 89; Cinefantastique, Vol. 27, No. 4/5, p. 92)
Another unused idea which also served as the basis for that two-parter was crafted by the writers because they wanted to avoid using time travel. "I had an idea where Sisko's consciousness gets disconnected from his body," stated Robert Wolfe, "and hooked into the mind of an ancestor with a similar genetic makeup, like two radios tuned to the same frequency. The idea came from the fact that my wife has been a counselor for the mentally ill homeless for a long time, and I've learned that just because they say they are something they couldn't be, doesn't mean it's not true for them." René Echevarria added, "Part of Robert's idea was that Sisko would see a cop and it would be Rene Auberjonois without his makeup. The homeless counselor would be Dax without the spots. Sisko would be seeing these blurry things and realize he was seeing through some weird filter. Robert wrote different drafts of the story with different tech." (Cinefantastique, Vol. 27, No. 4/5, p. 92)
A crossover between Deep Space Nine and Star Trek: The Next Generation was originally considered as one way to conclude DS9's first season. In the story, the two crews would have opposed an intergalactic invasion force. The plot was vetoed by Rick Berman. (Cinefantastique, Vol. 24, Nos. 3/4, p. 108)
Day at Quark'sEdit
Ferengi prejudice storyEdit
One of the three story ideas submitted by Armin Shimerman, Eric A. Stillwell and David R. George III dealt with prejudice and Ferengi. Referring to this plot concept, Shimerman noted, "Of the three pitch ideas, I gravitated to the one that was most interesting and upsetting." At Shimerman's suggestion, he and George turned the pitched story into the novel The 34th Rule. (Voyages of Imagination, p. 245)
Iliana Ghemor returnEdit
Some undeveloped stories involved the character of Iliana Ghemor, from DS9: "Second Skin". "I've heard several pitches where people want to find the real daughter, so obviously quite a number of people were struck by [the episode]," commented René Echevarria. (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 85)
Ron Moore's original concept for DS9: "Soldiers of the Empire" was for Worf and the crew of the Rotarran to enter Gre'thor. (Star Trek: Deep Space Nine Companion) While ultimately unused in DS9, this concept was later developed into VOY: "Barge of the Dead". (AOL chat, 1999)
Ronald D. Moore advocated doing a musical episode. "Oh, and I was agitating for a musical, man," he stated. "On record, I wanted to do a musical version of Trek well before Buffy or Chicago Hope. I wanted to do a musical episode, and nobody would f***in' do it." When the interview spoke of how this was accomplished on Buffy the Vampire Slayer, Moore responded, "Yeah, that's all we needed to do. There's just some tech virus that infects the crew and they can only communicate in song, you know? And just do it! And have a ball. That was part of the struggle on Next Gen, too, was to just have fun. 'Can we just do a laugh for an episode? Where it's not so serious, where we [don't] have to put the ship in jeopardy every week, where someone's life hangs in the balance. Let's just do a comedy episode.' And that was a real – they fought against it and fought against it and fought against it." 
In 1997, Ira Steven Behr commented to Star Trek Monthly, "You know the Nausicaans? They'll be back, and we'll do a show about them being an enemy for an episode." ("On Things Past, Present and Future", Star Trek Monthly issue 30)
Persistence of VisionEdit
A story written by Robert Hewitt Wolfe for DS9 Season 2 was inspired by he and Ira Steven Behr having a discussion about virtual reality, Behr asking, "How scary is it going to be in the future when you won't be able to tell what's real and what isn't?" Wolfe's subsequent story had Miles O'Brien and Jadzia Dax entering a virtual reality prison. The pair seem to escape but then realize they are still in the prison. "Then they escape again," Wolfe related, "and I wanted the tag to be where Keiko was telling O'Brien how good it was for him to be back, and O'Brien saying, 'I don't know whether I'm back or not. I'm never gonna know.' Fade out."
Michael Piller forced Robert Hewitt Wolfe into discarding the story, instead writing the similar Season 2 episode "Shadowplay". Although both stories featured the character of Rurigan, "Persistence of Vision" focused more on him and was considerably more downbeat. Some of the plot was reused in third season opening two-parter "The Search, Part I" and "The Search, Part II". (Star Trek: Deep Space Nine Companion, pp. 122-123) Additionally, the title "Persistence of Vision" was reused for an installment of Star Trek: Voyager.
Ro Laren returnEdit
The writing staff of Star Trek: Deep Space Nine briefly considered and discussed creating an episode which would have featured Ro Laren, who had defected to the Maquis in TNG: "Preemptive Strike". This undeveloped DS9 plot would have featured her in the Maquis. "The story never worked out," noted Ira Steven Behr. As a result, the group of writers instead wrote about Thomas Riker, newly defected to the Maquis, in the third season episode "Defiant". (Cinefantastique, Vol. 27, No. 4/5, p. 98)
Jack Treviño and Toni Marberry sold three stories to Deep Space Nine, but only two were filmed. The third story, sold about a year after the team sold "Little Green Men" and "Indiscretion", was called "Quorum". However, it went unproduced.  
A story that never made it in the script stage would have a swarm of space locusts heading for Bajor, the Bajorans unwilling to defend themselves because prophecy foretold the event. The staff never found a way to make the locust angle non-goofy, but locusts were eventually included in "Rapture" as a sort of in-joke. (Star Trek: Deep Space Nine Companion, p. 306)
Sito Jaxa returnEdit
One story considered by the writing staff concerned the return of Sito Jaxa from TNG: "Lower Decks". The pitch had Sito being imprisoned under inhumane conditions and suffering from post-traumatic stress disorder. Robert Hewitt Wolfe developed the story for some time. Feeling that there was insufficient explanation of Sito's condition, he had Sito killing her cellmate, whom she'd become close to. (Star Trek: Deep Space Nine Companion, p. 326) According to Ronald D. Moore, "We talked about this for quite awhile, but then decided that bringing Sito back would rob 'Lower Decks' of a great ending." (AOL chat, 1997)
Thomas Riker returnEdit
After "Defiant", Jonathan Frakes lobbied the producers to bring back Thomas Riker for a sequel episode. Frakes noted, "I keep thinking Tom is coming back [....] Don't you think it makes sense for them to send Kira over there to free Thomas? It's a no-brainer." Frakes, however, received no definite indication from the producers. (Star Trek: Deep Space Nine Companion, p. 191)
The Star Trek: Deep Space Nine Companion (pp. 191-192) states that, in the fourth season pitch letter sent to freelance writers, Thomas Riker was listed as a subject that the producers were not interested in hearing about. However, the authors note that this could have meant that the producers were already working on such a story. Several comments from Ronald D. Moore indicate that the writers did seriously consider the possibility. In a 1996 edition of Cinefantastique magazine (Vol. 27, No. 4/5, p. 98), Moore remarked, "We might see him again. We haven't really discussed the story, but we have talked about rescuing him someday." Similarly, in the 1996 book Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages (p. 87), Moore commented, "We'll probably see a return-of-Tom Riker episode. What's nice is he's not really a part of Next Generation, so he's ours, and we can do what we want with him and not worry about what the movies do with Will Riker." Likewise, in an online chat with fans, Moore noted, "Tom Riker may or may not get rescued at some point." (AOL chat, 1997)
In an interview with Jonathan Frakes provided with the TNG Season 6 DVD box set, he states that he had approached Moore regarding a Thomas Riker episode involving Damar's rebellion. However, the character never appeared again.