I worked on Babylon 5 for a period of time and even back then during the making of the original series the Producers talked about doing a major motion picture. I wouldn't put it past them, and I think there is a market for it.
With the 'Harry Potter' franchise nearing an end, WB very much wants to build new franchises, hence the talk of a 'Babylon' movie and the 'Tomb Raider' reboot to add with the various superhero franchises they have in the pipeline.
I was a huge fan of the series back in the 90's but since the sad deaths of Richard Biggs (Dr. Stephen Franklin) and Andreas Katsulas (G'Kar) I just can't get enthusiastic about new Babylon 5 adventures.
I'd say a movie could survive without Franklin, but not without G'Kar. Having said that, it's a part that could be recast, without any disrespect to Katsulas -- who was simply brilliant -- given the sheer amount of makeup and prosthetics involved, and not be too jarring a change.