I think it's important to really understand why the Wii succeeded, and to understand the expectations the successor could even have. In my opinion it would be impossible for the Wii U to do much more than half of what the Wii did numbers wise, simply because the wii exploded due to Wii sports. Wii sports was EVERYWHERE, the system was purchased at large to play that game and that game alone. It attracted a lot of non gamers, but as we saw they didn't tend to buy many games, some IP succeeded like Wii sports, Wii fit, Just dance, and then companies like MS and Sony jumped in (with some success it seems) to eat their lunch. The Wii sold to casual moms who barely buy games, kids, and hardcore Nintendo fans. The same fans that made the Gamecube era profitable for Nintendo, will be able to do the same for Wii U I imagine. The system should still sell at least 2x the cube, or half the Wii, probably ranking as Nintendo's second or third best selling system in the end, and if it has a short life span (I'm guessing 4-5 years while they launch a system to equal the MS/Sony stack in time) then that's more than enough to be a money maker for them. I very much believe Nintendo wants to be in their own generation while still being able to catch the others off guard.
I think people are being unfair to Nintendo though, it's not easy to just make an industry changing system or game, and they managed to do so in one shot with the last system, but you can't do that on a whim every time. I'm just sad that they didn't continue their push to expand and enhance motion controls and instead opted for a much less interesting touch screen mechanic that seems much like the Wii, not as valuable or neat in practice as it might be in concept. Nintendo has failed in one way with the Wii U, and that's creating a captivating way to really use the concept out of the box. Wii sports might have been largely inaccurate and smoke and mirrors, but it gave the illusion of something while being pretty convincing and still using new technology, but it never got to reach its full potential and to me, the Wii U seems like a step back in that sense. I can imagine much more compelling uses of a perfected Wii remote than a touch screen controller. Of the time I've spent with the Wii U, i'm not seeing it doing a lot of things the DS and modern day phones haven't already done, motion controls were new and exciting even if they didn't pan out well, and this console was never exciting to me on that level, only to finally get an HD Nintendo platform with a controller with more buttons.
Probably not the best place to rant, but I don't think Wii U is doomed, it just won't be another smash hit that initially dwarfs the Playstation 2 in popularity, for awhile the Wii looked like it would become the highest selling system of all time.
