Winterthorn: I haven't gotten to look at T20 yet (what can I say, my plate is full!) but I fully intend to. Some of it might work well with a B5 d20, although my impression of Traveller overall is that it puts a lot of detail into realistic technology, where I feel B5 is more about story, and sometimes happily ignores realism by simply declaring certain races "more advanced" and leaving it at that.
I don't necessarily think d20 Modern will be just right, though parts of the rules should be usable. The "Fast Hero/Smart Hero/etc." doesn't really fit B5, a universe where every character has a definite, specialized role. It seems more applicable to a setting where there may many characters of a similar background that need to be differentiated, such as Buffy: TVS (all the characters are HS students). Using d20 Modern for B5 would, I think, result in 420,000 Prestige and Advanced classes to replicate the abilities displayed onscreen during the series; why not just create a set of appropriate core classes at that point?
And about issues with B5 liscensed stuff disappearing before being released: Warner Brothers seems to be very strict with this particular liscense, pulling it from both the B5 Collectable Card Game and the very well done B5 Wars Starship Combat Game.
(Side note: If you want the B5 Wars tactical game at dirt cheap prices, AOG has to sell their entire inventory by 10/31 or then destroy it. Check out
Agents of Gaming for details. I can't recommend this game enough for B5 fans!)