I Quote the following news
Niitsuma confirmed there will be DLC of some sort for MvC3, what exactly will be in these packs hadn't been decided yet though.
Certain character combinations will enable you to do things that you otherwise wouldn't be able to do. Also, Niitsuma specifically said that they're pushing the individualism of the characters much more so than they did in Tatsunoko vs. Capcom.
Capcom would have to go back and renegotiate another contract with Marvel if they wanted to create an arcade release of MvC3 or other ports.
Disney buying Marvel has had no impact so far on the development of the game.
Marvel must approve everything Capcom does. From actual character actions, names of the moves, marketing and promotion and even if they hold live events, Marvel must give their OK.
At this stage of development, everything is pretty much locked down as far as the characters and features they'll be able to put in the game, but it's possible in the future, they may be able to add in fan requests and other things via DLC, but the schedule is locked down for as far as launch stuff is concerned.