Pikmin 3 is also mentioned as one of the titles being worked on.
http://www.nintendoworldreport.com/news/28887
Shigeru Miyamoto is working on an unnannounced, original title, the designer confirmed in an interview with Zoomin Games.
In the interview, Miyamoto talks about the legacy he has at Nintendo, explaining that many of the developers behind Super Mario 3D Land were once kids that grew up playing Mario games.
Near the end of the interview, it is confirmed that Miyamoto is working on several titles, including Pikmin 3 for the Wii U, Luigi's Mansion 2 for the 3DS and an undisclosed original title. The report doesn't mention which system is the game for.
The full interview follows:
Though i'm betting he is trying to pull a new Wii Sports/Nintendogs.
I agree with others.
Wish it was a new character, but it is more likely a new "concept" instead. Don't get me wrong, the guy is obviously the greatest genius in all of gaming ... the deity of all that is digital bliss... but it'd be nice if he came down to Earth once in a while and breathed new life into the familiar. Instead of simply uncovering my unknown desire to, for example, tilt my body until little spheres fall in designated holes.