In an interview with Associated Press (via Gamespot), Nintendo executive and creative visionary Shigeru Miyamoto mentioned that divisions within Nintendo are hard at work on new console ideas - but that the Wii U is still very much the focus.
"We're focused on providing a robust line-up of Wii U software for next year," he says. "It seems like we've managed to do that this year and people are very happy with what we've done on Wii U. For the time being, our focus is on the Wii U hardware, but Nintendo as a whole has groups working on ideas for new hardware systems. While we're busy working on software for the Wii U, we have production lines that are working on ideas for what the next system might be."
Whatever's next, Miyamoto wants it to launch with a new Mario, it seems. "From early on, I wanted Mario to be that character in the digital world, so that with each digital evolution, he was there to usher in the next era," he said. "I think that maybe when we release the next hardware system, you can look forward to seeing Mario take on a new role or in a new game."
It's pretty normal that Nintendo's R&D department would be playing with hardware ideas - the company is well-known for hardware experimentation, and the Wii U itself may well have been around as an idea since Nintendo's experimentation with second-screen functionality on the GBA and Gamecube.
Miyamoto also talked about the Wii U games that he personally is involved with at the moment, like Zelda and Star Fox. "I like to create gameplay mechanics more than I do stories," he says of the new Star Fox. "The story might not be too different from past Star Fox games, but the gameplay mechanics are going to feel very different because of the two-screen system of the Wii U with the GamePad and TV screen. It'll make for a very fun and unique way to play."
As for Zelda, Miyamoto told Associated Press what we already know: that it's returning to an open-world structure. "I can't talk much about it, but one of the things we're working on right now is that, as you play, the world will change and be affected by what you choose to do," he added.