The problem, in my opinion, is pincipally one of making sure it's a story that really works. That means not simply a story but a very good story that ties in very well with Bab5.
It would be great to see some of the original central characters - G'Kar and Londo most especially - but my personal perception is that anything too close to the end of series 5 will be in danger of looking conceptually messy.
That, to myself, rubs out the Telepath War as an option - although it would be great to see main characters, it's perhaps better to leave a good job finished badly, than try to add extra bits to the end in a well-meaning attempt to improve it.
Picking up on more distanced plot concepts would perhaps be the most valuable - not simply for Babylon 5 fans, but also for introducing other people to the concept. Showing something of the original Shadow War (option 2) could be very useful there - it could serve as an excellent prologue to Babylon 5 overall - there's certainly plenty of information that could be tied in from the original Bab5 seasons into it. The question is, how much can you actually do with a prologue that's worthwhile?
As for Crusade - that's over my head - and will be for a lot of people outside of the US, I suspect. So I'm not convinced it could possibly market well (ie, "here's a film about a story arc many of you won't have seen, won;t know about, won;t care about").
Fall of the Interstellar Allance - well, again, this sounds too close after Season 5 (unless I miscontrue the concept), and - let's face it - unless it's the Shadows themselves who physically destroy it, then the only other options of the Shaodws angry little brother, or a drawn out political process that could be meaningless to most viewers.
New Earth Chronicles sounds interesting - set far into the future, yes? In which case it could be like a clean break, and a good point from which to launch a whole new set of characters and even a series. If it involves the topic of humans evolving into angelic form then there's room for J Michael Straczynski to return to his own spiritual insights, and make a very meaningful story.
So, looking at it, the last option to myself I see as the one with the most potential - not so as to try and close the chapters of a book already written, but to open a new book related to the first, carrying it's strengths, but abandoning its weaknesses.
2c
