Some dude is leaking a ton of info about the game on Twitter. No proof that it's legit of course, but it's all pretty specific so it definitely sounds real. If this guy is for real then the previously rumored roster with Hsien-ko, Haggar, Akuma, Phoenix, Sentinel, and Taskmaster, with Galactus as the final boss is the real roster.
Some interesting tidbits for people who doesn't want to read the whole thing:
Hsien-ko and Phoenix will be the characters revealed this weekend at Jump Festa, the rumor about Phoenix being revived as buffed Dark Phoenix if Hyper bar is maxed is apparently true.
Capcom was originally going to bring back Venom and Cyclops but they were nixed by Marvel.
Human Torch was originally going to be in the game, but the constant flame effects + his specials/supers was just too much memory consumption and caused online lag, so he was cut and his work was rolled into Super Skrull and Phoenix. Marvel suggested Super Skrull in the first place after they encountered this problem.
Frank West was also in the game and then cut for 'technical reasons', apparently his zombie-related moves also caused a lot of online lag due to memory consumption. Sounds like he won't make it back in as DLC either. Frank being cut meant that somebody from Marvel needed to be taken out to keep the sides even, which ended up being Shuma-Gorath. So Shuma's done but Jill isn't, but it doesn't sound like either will be on the disc or anything like that.
Mega Man was cut pretty early on, surprisingly. He apparently just 'didn't add enough' to the game as a fighting game character. He was replaced by Arthur.
Niitsuma loves Darkstalkers just like every other dude at Capcom Japan, which is why we ended up with 3 DS characters.
Characters that were considered but didn't make it in: Juggernaut, Silver Surfer, Thanos, Elektra, Strider, and M. Bison. Doc Ock and Blade were also considered, but left out because of too much similarity to Spencer and Chris/Dante respectively. Possible that some of them might make it in as DLC, but who knows.