I haven't heard anything about any Mega Man 10 co-op play online... but I definitely think it'd be a cool idea.
 
Imagine running around with one player being Mega man and the other being Proto man
 
I think it's a neat idea, what do you guys think?

Co-op is always a blast, but when you mentioned Mega Man and co-op, I instantly thought of Rush. Does this make me a bad person?

How about NO.
 
Developers need to stop wasting time with multiplayer modes in games that don't need them.

 It has been rumoured:  http://www.giantbomb.com/mega-man-10/61-29413/mega-man-10-will-feature-a-two-player-mode-rumour/35-377450/#5
 
I would be in favour, depending on how it's constructed. I could see them implementing some form of spawn mechanic (MM has the cutest spawn animation ever), one that could allow a second player to select spot on screen and spawn in or out of levels which have been specifically designed for two player gameplay.