Emulators use roms, don't they? Which I can't find anyway. Not of Xbox or anything like that...
I think the main problem would be that the Wii doesn't really have a gamepad, and while the Wiimote is good, not all genres of games could really work so well on it. I couldn't see myself palying an Oddworld game on it, unless maybe with a GC remote...but I doubt a game like that would ever be released, unless it came with a cool custom GC remote...

DO IT OWI, DO IT. If it's multiplatform, at the very least...otherwise, gimme a free Xbox 360.
I CAN'T CHOOSE=PAIN.