[igotrhythm]

I'm gonna say in with Zero, out with Megaman. Why? Megaman just doesn't have the diverse move set required of characters in games like this. (See the reasoning behind why he wasn't in MvC 3.) Plus, you know you want to see screen shots of Zero holding an item-drop beam sword. I'd say Megaman X would be a cool assist trophy provided they could get the rights to the IP from Capcom.

As for other suggestions, you kind of have to consider what niche the character would fill in the roster instead of just thinking "zomg this would be so cool!" If they got rid of Samus changing forms with each use of her final smash, I'd like her a whole lot more, as they play completely differently. (Don't even start on Pkmn Trainer requiring mastery of THREE styles...)

On the subject of sword wielders, Takamaru from Mysterious Murasame Castle would make a good addition as a trophy or character. Anyone who's played with him in Samurai Warriors 3 knows that there's a LOT of potential here for filling the Noob Saibot role of combo-whore + reach. You've even got a lot of regular and special attacks, including the "final smash" all animated in a way that the Wii thinks it can manage. If he ends up as a trophy, there's some competition in each of the niches between Samurai Goroh and Lyn, and you even have a pre-made adventure mode if you go that road!

As for who to take out? Definitely Sonic. He was shoehorned into the campaign mode at the last possible moment, and one has to wonder what the hell he's doing in a Nintendo game when he was invented specifically to give Mario and friends a run for their money? His final is incredibly cheap, his dash is impossible to control, and I think he can string aerial specials to some extent before going into helpless as if that's fair compensation for his lack of reach and power.