http://wiiublog.com/retro-is-hard-at-work-but-nintendo-is-not-going-to-talk-about-what-theyre-working-on/
In an interview with Reggie Fils-Aime, IGN asked him what Retro Studios is working on. They’re rumored to be working on a Wii U title that “everyone wants” them to do. But for the time being, Reggie only said that:
…if I disclosed what Retro is doing, I would have the president of Retro literally calling me right now saying, “Reggie, what are you doing?” We love that people are interested. We love surprising people. I remember getting the questions before we announced Donkey Kong Country Returns. And I loved unveiling that. So… Rest assured, the team is hard at work. But I’m not gonna tell you what they’re working on.
And so the waiting game continues.