If they get a few big 3rd party characters, this game is gonna be fiyaaah.
Solid Snake (no brainer really, pretty much required)
A Final Fantasy protagonist (Square would most likely part with Lightning... and the game will probably need help on the female roster anyway)
Ezio or the new Assassin from AC3
Leon S. Kennedy (he's not in MvC and he's coming back into the spotlight with RE6)
Lara Croft (She's also coming back with a new game)
A Big Daddy variant
Isaac from Dead Space
That's my short list for 3rd party characters. Half of them were actually in that PS3 commercial from a few months back, so there's already a dialog there. Naturally they should try and get 1 from each big publisher. Can't wait

Let's goooooo!