The Quarter Bin, next week's Comic-Con in San Diego (Earth-616) will host the announcement of "Ultimate Marvel vs. Capcom 3."
We know that Marvel vs. Capcom 3 producer Ryota Niitsuma will share some news at a Marvel vs. Capcom 3 panel on Saturday, and that Marvel Interactive will have its own panel to discuss several upcoming games, along with "some exciting new details about the future of Marvel vs. Capcom 3." Since Capcom's unlikely to comment before those panels take place, this rumor is hinged on the singling out of MvC3 over the franchise as a whole. (Another possibility: A PC or portable version of the same game.)
Still, The Quarter Bin stakes its reputation on the assertion that Capcom will repeat its Super Street Fighter IV strategy and launch Ultimate MvC3 at a discounted price ($39.99), with 12 extra characters added to the original roster. We remain skeptical of this rumor -- not only have we been unable to turn up any domain registrations for the title, but the Earth-616 Capcom would surely go for "Penultimate Marvel vs. Capcom 3" first.
Update: As expected, Capcom gave us its standard response. "We do not comment on rumors or speculation."
Update 2: It's real.