megaman would be hard to fit into smash bros unless they gave him abilities from baddies in previous megaman games.
His biggest strength in his games were that once he defeated a boss, he gained their abilities... you can't technically do that in smash bros since the other characters aren't robots and don't have the chips he needs to take their abilities.
Megaman without extra abilities sucks
Sure, you could put him in just as normal megaman, with all his own abilities maxed out, but then he's just a weaker version of samus.