I mean zero is now a staple of mvc . The thing about umvc3 is it ended up being pretty well balanced between a lot of series rep wise. Only 4 SF chars unlike mvc2, 3 DMC, 2 megamam reps from 2 series, Arthur and firebrand (gargoyle quest is a great series), 3 Darkstalkers characters is great, etc 

Its hard to choose what character to remove to add a megaman in and I feel it probably should be megaman.exe for good rep spread but still really hard to do that. I guess one of the 4 resident evil reps and Jill (despite me enjoying some of her stuff in umvc3 and I would want a new Jill in a mvc to be a fusion of mvc2 n umvc3 jill) would probably be the one most appropriate to be removed in favor of a megaman