While we're speculating on developer and roster, I just wonder what they'll do with voice acting.
On one hand, MvC3 isn't THAT old and it would make sense if they wanted to save money and just reuse voice samples (and MAYBE bring in the voice actors to record a couple new intro lines like Ultimate)
Back when MvC3 was announced and the first footage was shown, they actually debuted new voice actors for the Marvel characters who would later voice the characters on Avengers Earth's Mightiest Heroes which wasn't out yet. I still remember people ripping on Brian Bloom's Cap for sounding like he was "mocking" the original MSH/MvC's Cap voice. Good times.
But NOW, they seem to have new definitive voice actors now. I'd imagine they would likely replace Greg Ellis with Trevor Devall for Rocket, Rick D. Wasserman with Travis Willingham (Guile!) for Thor, and Eric Loomis with Mick Wingert for Iron Man (Adrian Pasdar is on his way out supposedly). But there's a couple that's going to be awkward.
Roger Craig Smith is THE voice for Cap now, but his Cap sounds almost identical to his Chris Redfield
Laura Bailey is THE voice for Black Widow which is just a slightly deeper, more mature sounding Chun Li (assuming BW gets in which is certainly possible)
Troy Baker is THE voice for Hawkeye now, but it sounds identical to his UMVC3 Nova
On the other hand, who knows what they'll do for Spidey. USM is ending, and the new show will likely have a new voice which will probably debut here.
Eh, just food for thought.