It's the successor to the 3DS that will be the issue there (hand-me-down phones and cheap ios games gobbling up their main demographic) but with the Wii U, if they don't want to go third-party next-generation, they'll need to put together at least 2 more games (not far from each other and with massive advertising) where:
1- the quality is just out of this world. The Nintendo games of our dreams. I absolutely agreed that next 3D Mario should have focused on including multiplayer, which they did it, but they let everything else slip in the face of problems with the camera. Easy way out is not out of this world quality. They want us to pay a premium for the console, the games need to be the very definition of premium.
2- make much better use of the gamepad with their games. Not touch-button triggers but whole games that revolve around the gamepad.
3- like 85% focus on family games. Especially with the advertising. No metroid. No f-zero yet [actually, F-zero too]. Maybe Starfox but bascially something new that the family can play together. It's the family system. We were sold on the Wii, and then we weren't, now we need to be really sold on the Wii U that there is something that the family can play and will last a decent amount of the gen.
Things like Mario Party but even more appealing. Nintendo Party Board Game Suite. Super interactive, lots of use of the gamepad, feels next-gen, lots of quality and content there and actually looks fun and well done (NOT SHIT, not a single mini game should be shit at this point, it's not THAT hard). & Kids can also play online with their friends (safely/protected), but local play is there too of course.
That's their main advantage. Family appeal. They're losing it and it's not really because of LBP, Tearaway and Puppeteer, but you can see people are trying to cover things for everyone too - like MS's awesome new PvZ shooter.
Nintendo need to be making the Banjos of 3d gaming again too.
Economy is tough, people can't shell out for everything like they used to, especially when they know what's up.
Nintendo HD please.
I don't think Smash and Mario have as good as a chance in next-gen year but it's doubtful that support will be slowing for those consoles.