But... but he said you have to see Diddy Kong in motion!
Anyway, it feels like Smash Brawl is trying to bring in at least two representatives of every major ongoing Nintendo series. The only one missing two characters is Metroid, unless you count Samus and Zero Suit Samus as two different characters, and I'm fairly sure another character will represent Fire Emblem and Starfox, though I doubt F-Zero and Earthbound will get the same treatment.
Anyway, yes, Mega Man would be the next best thing after Sonic. It's unlikely, but I think it'd be awesome that if Mega Man is in a Smash Bros. game, all his alternate costumes would represent the other Mega Man series (since he changes colors anyway when he gets someone's power and we can't have that happening in a VS. game, think of the confusion!). Yup, Mega Man, X, Megaman Trigger, and even that MegaMan.EXE all fighting eachother at once. Oh my that would be too much, I'd probably just change their helmet to look like the other spinoff series if I was the one who was in charge of putting him in just because the former suggestion would dehydrate every living human of their semen.