I'm betting a large chunk of this roster is going to be based on Curtain Call's roster and that's not really a bad thing as it covers a lot of good and important characters.
As long as they don't ignore FFVI, which they did with Duodecim and one reason why I didn't buy the game, I'll be happy. They ignored FFIX as well.
Games like this are all about serving that fanbase and giving them the characters they want. It's why Super Smash Bros. is the big hit it is today (and yet people still complain about not getting the Nintendo characters they want). Final Fantasy just so happens to have a large number of characters people like who are not the main protagonist and villain.
It has me pretty excited that they're shooting for such a large number cause it tells me that they understand this. Admittedly, it's probably the only reason I'm excited for this right now too.
They should do fan voting like Nintendo is doing with Super Smash Bros. too. See what characters fans really want.