Well first of all Capcom insider Kensk said that Nitsuma's Darkstalker deconfirmation should be "re-read" again. He later insisted Hsien-Ko, Taskmaster, and Haggar were surefire bets.

I take these deconfirmations (actually dis-confirm is the proper word but deconfirmed just rolls of the tongue better) with a grain of salt because if someone asked if they were in the game, why would Nitsuma say they were? He'd want to keep it a surprise, wouldn't he? Unless there was an actual explanation behind it like Ghost Rider and his bike, or the F4 being replaced by Super Skrull.

And it seems like new characters WILL be added for DLC. I imagine a lot of TvC and MvC2 conversions would be the likely candidates.