From the look of things, it's probably a game with some weird customization things involving other capcom games you own. There's nothing in the commercial that even hints at a multiplayer capability -- the mmo rumors are just the result of wishful thinking, I'm guessing.
Maybe it's a crossover game like the super mario crossover that's been gaining in popularity? Play as Ryu for a level, or switch to the knight guy or back to megaman for some portion. That might be cool.
Finally a reveal of what the game is about. It looks like you make your own mix and match Megaman style character using various parts you've gathered (which effects powers, abilities, and stats), then run them through player and Capcom made Megaman levels to earn more stuff. This looks like it could be fun, but I hope it's going to be a Xbox Live Arcade/PSN title and not a $60 disk title.
You can watch a gameplay trailer here. And yes, that IS The Megas playing "Message from Dr. Light" in the trailer. No one is saying if they are doing music for the game or not (though it would explain why the Megaman 3 album has been delayed) but maybe we'll get lucky.