I think Wii U will do pretty good.
It can get close to 100 million if Wii U does get serious 3rd party support.
It`s possible that Wii U might not be as hot as Wii was, because of the controller. But Wii remotes are still there; the Wii U gamepad, despite more complex, has some resemblance to a tablet and that is good for Wii U; and of course, asymmetric gameplay might just be fun enough to actually interest people.
But, even if Wii U doesn`t get the same casual/non-gamer support Wii had, it can recoup it`s losses with the Wii owners who did buy and HD console for... well, pretty much everything Wii did not have (online play, HD graphics, 3rd party support) and that could really hinder PS4 and Xbox 720.
More, so far, and seeing as there really isn`t anything concrete on MS and Sony`s next consoles, it`s hard to predict there moves.
On MS side it`s easy to see a Kinect 2.0 and a regular controller (probably with a screen on it), suppport for Smartglass. Problem is, all won`t be anything new when the console is released.
Kinect is already a holiday seller and i honestly doubt a better version will work for Xbox720 the same way Kinect worked for XB 360.
In essence, if all MS introduces next generation is better versions of existing products i honestly don`t see how that could work for them to really push consoles.
PS4 will be in the same situation. More of the same or something new?
What differentiates Sony from MS, for me, is that, with time, Sony pushed PS3 so well, that the playstation brand became very strong on home consoles - less in the States, to be fair. And that could really cause some damage specially on MS`s side, because, if they do release around the same time, Xbox won`t be the only HD console, only true Online play console, like 360 was for more than it`s advantage year, but also that one year of lead on a very important period for home consoles.
The way i see it is that introducing something new without competition worked really well for MS. Yes, Sony did some serious mistakes, but still, even without those, MS would have still pushed 360 as a serious competitor because it had the time to spread the word on how only 360 could provide online competition, HD graphics, an HDD, great 3rd party support.
Wii U gets the same chance that MS had to position itself as unique and that it can really get 3rd party support like in the old days.
If things work out for Wii U - and it`s launch line-up is already a clear indication of that - it can be first next generation.