Not to bomb you with Square-Enix news, but have you noticed that they're working on a Final Fantasy themed game for the PSP called Dissidia: Final Fantasy? The gameplay sounds like a two-player fighting game but apparently it's got a script "double the length of Crisis Core".
This is actually last year's news but somehow I completely missed it, so it's not beyond possibility that you have too. The massive downside, of course, is that you'd have to fire up a PSP in order to play it, but I know some of you out there are masochistic enough to do that so presumably you'll be stoked when Dissidia hits stores.
Yes, Sephiroth is playable.