Isn't 720i the same thing as 480p?
Regardless, the issue is that the Wii can not, can not, can not, cannot, can't output anything above 480p. It's not built to out put anything with a higher resolution. It can't do it. It can't do it. It can't do it.
Regardless, you're probably basing this off of that Street Fighter II HD Remix. Know that that's a remake. The engine of the game has been reworked, the attacks have been altered, and the enter game is being built from the ground up. Remake of that proportion is possible, just not in the kind of high definition you reference here. It's entirely possible, and up to developers to make if they want to, and publishers to fund if they think it'll sell.
Additionally, I think you're mistaken on what the Xbox and PS2 could output, but I'm not sure and right now, I don't care enough to look it up. I could very well be wrong, though.