CG tech has certainly advanced enough (beyond the days of Amiga Video Toaster, which was what B5 first used for its CG space stuff) that a B5 big screen event would look gorgeous. Granted, as time went on for the show, the visual aspect advanced a lot, but with today's tech, B5 would be a visual feast on the silver screen.
I would think that a telemovie like "In the Beginning" where we see the Earth/Minbari war would be a good start, if it got a big screen re-translation, both in terms of story-telling and visual effects. To be big-screen, you have to THINK big screen. (This, to me, was the problem that marred the first three Star Trek TNG movies---Generations, First Contact, Insurrection).
Now, with the full on visual overhaul....
Either do a full telling of "In the Beginning" and be its own movie, or have it be, perhaps, the first ten minutes of the movie, told in a quick historical perspective. Then, we get a quick rundown of how Babylon's 1-3 were built, and quickly destroyed before going operational. You could have Babylon 4 come on line, and then, as in the series mythos, 24 hours later, it disappears. Now, granted, I know a story was done on this in the show, but perhaps they could redux it, give it a different angle, and then that's where the more successfully operational B5 and her crew come into play.