Update: Shacknews was able to confirm with Capcom that there are indeed more character announcements on the way for Marvel vs. Capcom 3. They were even able to nail down the time line, as a representative of the company had this to say.
All will be revealed in the next couple of weeks.
Earlier: It was mentioned on the official Marvel vs. Capcom 3 website that more characters would be announced for the game in the future. Here's the graphic.
Click image for larger version
Previously, it was stated there would be two more fighters announced to fill out the 36 person roster, which ended up being Sentinel and Hsien-Ko, so the logical jump is that these new fighters will be DLC.
Capcom recommends following their Facebook and Twitter pages for more news in the future.
Sent in by Blaidd.
Source: http://www.eventhubs.com/news/2011/jan/28/more-characters-be-announced-marvel-vs-capcom-3/
Hopefully, Vergil (Devil May Cry) will be included as a DLC character, along with Leon (Resident Evil), Gene (God Hand), and other popular characters.