I've seen this idea tossed around, even lately by Patrick Kelpick, but I had conceived of this before.
The Wii U is struggling and the 3DS is alright. Nintendo has to split it's development capabilities between the two, and one is suffering more from it. In this day and age, of extremely powerful mobile devices, Nintendo needs a change.
ONE CONSOLE. ONE TO RULE THEM ALL.
What excites me about the idea of Windows 8, is that you can theoretically do everything on it, Metro Apps for quick bite sized app functionality on the the go or for play, and intensive windows applications when you need them. I have a Surface Pro, I use it like a play tablet, but I can also pop open full photoshop on it and rock some photos out of that beast. Nintendo needs to adopt that sort of mentality.
The Wii U tablet is an egg on the face. It's nice, but too niche to bail out an underpowered system. Meanwhile the 3DS is a little underpowered and cheap, but has good enough games with a portable mentality to bail it out.
They need a hybrid device, that they can make all games for.
A more powerful hand held, that comes with a TV set top box that streams the games to the TV. Essentially combining the Wii U and the 3DS into one console that can be supported by Nintendo's full development force. Perhaps the set top box has some extra GPU that could natively upscale the hand held games to look better on the Television, I don't know. But Nintendo no longer has the chops to full support a home console when they're biggest strength is games.
I have a 3DS that I enjoy, and I wouldn't mind a Wii U, but accounting for how I would only ever turn the Wii U on to play a specific game every few MONTHS, I'd simply rather put the money some where else.