Obviously there were never any such movies made, and never will be. But I'm interested in how far any planning ever went.
What were the firmest any plans to produce a movie featuring DS9 or Voyager got?
There is no evidence that any of the major creative staff behind the TNG-DS9-Voyager era — Rick Berman, Brannon Braga, Michael Piller, Jeri Taylor, etc. — had ever planned films for either DS9 or Voyager. If there were plans, even very preliminary ones, they were never commented on publicly.
Of course, there must have been at least some discussion amongst the creative staff. Here are my speculations about how these discussions would have played out:
All in all, both DS9 and Voyager would have been better suited to a television movie or a further mini-series than to the full cinematic treatment.
But then hold on...
Voyager actually had a television movie, titled Voyager: Dark Frontier. It was a feature-length, made-for-tv movie. It aired during Season 5, but was advertised officially by the UPN Network as a movie:
VOICE-OVER: The Voyager movie you thought you'd never see...Voyager: Dark Frontier, a Star Trek movie event.
Because the film now airs in syndication as a two-part episode, many have forgotten that this was a genuine made-for-tv movie.
While there wasn't a plan for a full-blown Voyager film in cinemas, there was an intention to include certain Voyager characters in Nemesis. Apart from Admiral Janeway's cameo, there were plans to have Jeri Ryan star in Nemesis, with Seven of Nine as an Enterprise-E crew member.
However, the actress turned down the role:
UPDATE (Aug 2017): This week, at the Las Vegas Star Trek convention, Marina Sirtis revealed the following about the Jeri Ryan in Nemesis issue:
"When I was negotiating for Nemesis they literally threatened to fire me and recast Troi, well not actually recast, but they said "We are going to fire you and hire Jeri Ryan (Seven of Nine from Star Trek Voyager)." And I said "Well Jeri Ryan won’t do it for that money, that is for sure."
There is some interesting discussion on the issue of making a DS9 film here:
Also, actor Garrett Wang (Harry Kim) discussed his pitch for a Voyager film, and how it was ignored, in this interview:
At the Star Trek 50th Anniversary Celebration in Las Vegas, Ira Steven Behr commented on the DS9 movie issue, effectively saying that such a thing was never in their sights:
BEHR: Even today, I still get the question: will there be a DS9 movie? I love the thought but even at the time, we knew that would never happen....At the same time, that gave us the opportunity to not worry about where the show was going to go in another iteration….We were just going to go the distance and end it as best we could. I think that last image of Jake and Kira looking out the window, there's so much going on in that tableau: hope, sadness, questioning the future. It seemed like the perfect way to end the series. The station’s still there. It’s not going away. It’s not pulling away, we are. It's getting smaller, but it’s still there. It felt like a good way to go out.