Ok...since the topic has changed COMPLETELY from the point of the thread I will join in.
Super Smash Brothers, could be done in a 3D enviroment, and it could be very very fun, but what you would have is less of a combo rich fighter and more of a platform fighter...which is what Powerstone was.
Powerstone was alot of fun, but it didn't have very much depth at all, because creating that depth meant much more complicated controls. What you ended up getting was simple button press combos, and fullscreen combos, and not very precise platforming elements. Not really a fighter, and not really a platformer.
I think Super Smash Brothers in 3D could be done easier and very fun, but it would also so dramatically change SSB that it wouldn't feel like SSB. Just how Super Mario 64 is a Mario game, but it doesn't feel like a Mario game compared to the 2D worlds.
I personally wouldn't mind Nintendo trying different things with the king of the hill formula of SSB in 3D...but for revolution only. And then for DS and eventually Gameboy Revolution (whatever) keep it 2D.
Online is another situation completely. I don't like online gaming, but creating a game online doesn't effect the playability of multiplayer at home, or single player. Or shouldn't.