Impossible to say. The Wii went viral because of interest from the casual market. I can't tell you how many middle aged people who had zero previous interest in gaming bought one because they went to a party and had fun with Wii Sports. The thing is, many of those people consider themselves set on consoles. They will have no desire to rush out and buy something new and improved. In their minds, as long as they can break out the Wii for company now and then, they're good.
There is also the possibility that the casual market will be turned off by the controllers. A lot of people shy away from things that aren't intuitive. True story, just yesterday I heard someone say that game controllers are "too complex"--something I've heard many times before, as have most other gamers. The Wii got around that, but I'm not sure the Wii U will.
I think the Wii U's demographic will have more core than the Wii but far less of the casual. I don't think it will go viral, at least not to the level of the Wii. Does that mean it will sell badly? Not at all. However, I think the Wii's sales rate was an anomaly and that it would be wrong to expect the same from the Wii U.
