During an interview with Famitsu magazine, Shigeru Miyamoto stated that Nintendo is working on a new Wii U game and that it is not one of the company's existing franchises.
"With Mario Kart 8 coming out in the Spring of next year, we'll have a good selection [of Wii U games] available, so I'm thinking isn't it about time we release a new franchise?" reads the quote. Famitsu's follow-up question - "A new franchise! Would that a be brand new title that you would be working on?" - garnered the following response: "I can't talk too much detail right now, but I will say that this new title has been keeping me busy lately."
This game would be the first new IP from Nintendo to be released on the Wii U, excluding Nintendo Land. Nintendo is best known for innovating and sticking with their core franchises.