Luigi's Mansion 3 for Wii u

I hope that's Next Level Games' next title. They've been working on a new game for at least a year and 8 months now, so it should be revealed soon. Or maybe they're waiting for E3 2015.

A new Diddy Kong Racing would be excellent.
A Duck Hunt reboot would also be good. Make it a 3D platformer similar to the N64 Banjo Kazooie games.

I want a open world game where you play a Rogue Toad battling injustice and corruption in the Mushroom Kingdom. We'll call it Watchtoads and we'll get the writers of Adventure Time on it.

Something like Paper Bowser, complete with all the humor and story Sticker Star was missing, would be completely awesome. Or maybe some other Bowser game as long as it's really funny.

However, if I've got to choose one it would be a Zelda game. You've got magic wielding, stealth action, an awesome setting, just so many ingredients for a really cool new IP that can cater to older audiences. Heck, throw in some RPG elements. Just make it something neat and different for a Nintendo game.