Re: Would DS9 have gotten a film version if it wasn't a Star Trek seri
The argument of poor ratings doesn't fly totally, IMO. Any film can be successful if promoted properly. I remember the Blair Witch Project many years ago, which IMO was the classic example of how marketing in itself can make high box office takings (the film stunk, but I'm digressing). The reason why films like Avatar got big is due to marketing and word of mouth.
That said, more often than not, for a big budget film (as any Trek film, nay sci-fi film, would be) the outlay has to be justified. If there is no big name star, or high TV ratings, or prior franchise/works to build on, then the outlay makes no sense. Most of the big films in recent years can build on at least one aspect, such as Transformers for instance.
All of the cast of DS9 were great actors, but neither were (or are now) A-list stars as such. And of course, it's ratings were never high and is not ingrained into pop culture as TNG is.