Personally for me if Nintendo announced Star Fox for the Wii U I would go out and buy a Wii U immediately, they wouldn't even need to show me any gameplay footage, I would just get one lol.  Seriously though I am dying for another real Star Fox game, we are long past due for one.  What is that one game for you?

Super Smash Bros. for Wii U is the must have for me, though I find others interesting, they won't make me buy it right away. TimeSplitters 4 would also make me buy it immediately, however I don't think that will happen.

Bayonetta 2 was the game that made me say "I have to have one."

Donkey Kong Country Tropical Freeze is the game that decided when I'd get one, as it comes out before Bayo 2 and I can't miss it either.

A third person action RPG where all of the mushroom kingdom guys are kidnapped by an ancient alien who wants to research mario's ability to use power up's and use it on his army to take over the universe, Bowser's life is shallow because now he doesn't have a reason to live (kidnap Peach) and someone else stole his job so is now his responsibility to travel through space and time gathering information, new powers and allies to be able to take down the alien overlord, now RESCUE Peach and inevitably Mario and crew, and return things back to how they've always been. That would make me buy a Wii U.

X would get me close, although i'm still waiting for more jrpg's

Initially I thought it would be 3D Mario but the catsuit isn't really doing it for me so I'll say kart

I already plan on getting a WiiU but if they make another Pokemon Colesseum style game I'd buy one tomorrow.

none of those games unless they evolve over their predecessors.

I think X does.

Ya I defently think Nintendo needs more studios like Monolith to make JRPGs for them or atleast double the staff at Monolith so they can make 2 games at once.