Please allow to really strongly disagree.
Well, it's highly alluded that 3 v 3 will be brought back, assists will return and the game will "combine the best of both MvC2 and TvC".
If that much is true, then I think the game will need to be 6 buttons. Though, it likely will be in the same fashion as MvC2, which could easily have those two assist buttons conveniently on the shoulder buttons.
If SF4 was able to get away with 6 buttons, and it's definitely a game that has a good deal of casual appeal in itself, then surely MvC3, a game that will thrive on its casual appeal, can do as such like it predecessor.
stuff
Again, those are GUESSES by Kotaku. A good deal are probably fine, like Super Skrull and Dante. But on the other hand, "Mephisto" could easily be some one like Dormmamu or (more likely) Ghost Rider.