First of all, yes, I believe that Wii is capable of selling 100M units. It could take years, but it will happen.
But I see no way that Wii U will sell even close to that amount. Let's look at the appeal of the Wii. It offered a new gameplay experience never before seen. It was something that no one saw coming, and that's the reason it sparked such enthusiasm and excitement.
Wii U, on the other hand, simply uses existing technology that everyone already has on their phones and tablets. Touch-based, and multi-screen gameplay isn't inspiring as much imagination in gamers and developers alike. Instead of setting itself apart from current gameplay options, it is borrowing from the market that already exists.
It wasn't the hardware capabilities of the Wii that pushed sales, nor will it be a determining factor for Wii U sales. The one and only sales hook is something that isn't actually new or progressive.
I don't see Wii U selling more than 50-60M units in its lifetime, unless there is a drastic price cut as some point (not unlike what happened with the 3DS). I see the situation with the Wii U much more similar to the 3DS than I do with Wii. Consumers aren't sure why they should go all in without a more appealing price or many more games that they've never seen before.
