Personally, I love the idea of a permanently bundled game. It is hands down the best way to turn an IP into a mega-success. Mario might be half of what it is today had it not been bundled with the NES, for example.
With that in mind, I hope they bundle something that hasn't been around for 20 years, even if it's a Wii U port. It should also be a real IP, not a glorified feature demo.
Nintendo should continue to separate themselves from PS/Xbox and I think a fun pack-in game with a lot of replay potential would contribute to that.