I never expected Nintendo Land to get near the success of Wii Sports, though then again few games have. I do agree Nintendo needs a game like Wii Sports to ignite interest and again reach the mass market, but a sequel to Wii Sports itself IMO won't do it. They'll instead need a game LIKE Wii Sports that carries the same spirit, and brings a new audience.
I'm pretty convinced at this point that no amount of sales for a Nintendo console will convince third parties. Wii at one point outsold the HD twins COMBINED by a large amount and one month sold 4.3 million units, yet still nothing changed. So sales don't really matter in that respect. I've given up on third parties on Nintendo consoles, and I have a feeling Nintendo has too. Luckily for Nintendo their games are strong enough that they don't really need third party support. They've shown they can sell 100 million without it.
Nintendo could carry a platform on its own with the Wii. But that was when games like Zelda TP, and the motion controls were super hyped. I have to say that I don't trust Nintendo's competence to replicate the Wii phenomenon on their own, at least not with the Wii U. Aonuma's direction is making the Zelda brand slowly rot away and other franchises aren't doing much better. To me it seems like Twilight princess and Skyward Sword has really hurt the Zelda brand. The minimal effort and lack of new content in the 2D Mario games are hurting that series too. Smash Bros is being outsourced. 3D Mario being mutated to try and replace 2D Mario is making it appeal to even fewer people. And don't get me started on Metroid.
I remember, that even though analysts and industry twats hated the Wii since the very beginning, regular people talked about it a lot, and I saw incredible potential. My gut feeling about the Wii U when it was revealed was very different, and regular people aren't talking about it, and there is this confusion about it being a new controller.
I am very worried about Nintendo's future with the consoles, and it's a damn shame because I don't think the third party industry would have survived if they ignored another Wii phenomenon. One thing that the Wii U does right though is being controller-agnostic, that is going to make it's sucess all about the games, third parties can make games for the controller they want, and Nintendo could theoretically re-enter the Wii path on it should they come to their senses. I think the performane of Wii Fit U will be extremely important.