According to the Team Spooky blog, from the same author behind the full character roster leak for Super Street Fighter IV last summer, Capcom is going to be making an announcement for Marvel vs. Capcom 3.
The post itself is mainly comprised of the author explaining how he had been banned from several places, but it does present some circumstantial evidence to support the claim.
If true, then the announcement is going to be made in May, although there is also Capcom’s annual event Captivate next week. Stay tuned.