This is actually something I've thought about for a while... or rather, occasionally, since I haven't been playing the game that long.
I love the characters, setting, and overall premise of Super Meat Boy, but every time I think of a sequel, one question immediately pops into my mind: what would a sequel add? What would the point be in a sequel? What could Team Meat do that they haven't already done with this game? ...And the original Meat Boy game on Newgrounds.
I feel like a sequel could be a waste of time and effort that could be put into making new, original games, as much as I'd like to see a sequel.
I will be happy if the hypothetical sequel was only more and better. I mean, more levels (marvellously designed like the original, of course), with more charachters. Nothing more, like an expansion pack.