A Retro game at launch would be nice, although I would probably like a new IP from them. Maybe an adventure FPS? Or an FPSRPG like Borderlands? They've got quite the talent to pull that off, and a new IP has a better chance of being a success at the start of a new generation. Also, didn't they have two teams at Retro? I remember readying something about that a while ago. Monolith Soft just opened a new studio near Nintendo's HQ, and apparently they're working on a 3DS game while the main team is on a Wii U game.
Then again, if Pikmin is a launch title, then other big Nintendo games, like Retro's project, would be pushed back. I'm actually hoping for an adventure FPSRPG from Retro. Combine Metroid Prime with Borderlands, and you have a winner for me. From Monolith, I'd love a drop in/drop out co-op, open world RPG, but with a lot of color. I can never get into the Elder Scrolls games because of the lack of color. It just feels lifeless and depressing. They did say that Skyrim would be the inspiration for their next project.