I think a way to link up to the internet (whether or not be broadband or wireless, pref. wireless) to download any game from the N64, to the portables to play on Revolution, plus backwards compatibility with the Gamecube, would be an amazing coup for Nintendo... Retro gaming is in, as Nintendo has seen with their NES classics series, something like that would get legions of gamers to stand up and take notice.
I'd like to see the following games, myself:
Mario Revolution - it's *GOT* to launch with a Mario game, even better if it's included with a system... I think this was one of the biggest fallacies with the Gamecube
Super Smash Mayhem - My friend came up with this name... But I'm a hardcore Melee player (our school had its own student association funded club for the game), and a new sequel would kick ass... with online support too, so I can play against my old college buddies on the other side of the state.
A big name RPG - Nintendo went from being THE RPG system (SNES) to having nearly none (N64). Most RPG fans play little else and will buy the system that has the most/biggest name RPGs for it.
A Zelda and Earthbound can come out later, but definitely promise them at launch... and don't radically change the style of the graphics... A lot of people were turned off on TWW...