The sales will no doubt start to pick up, but will it reach anywhere near the sales of the Wii?  I don't think so, I think it will get around 30m, same as the N64 and GC.  I'm pretty sure Nintendo can still make a profit with that number.

If by "turn the Wii U around" you mean people will actually buy it...yes. Of course.

But if you mean the system will actually turn around and start selling respectably, then no, I can't see that happening. Definitely not on the strength of Smash Bros alone.

HOPE!!

For the WiiU's sake I hope Super Mario 3D World is the one that permanently turns things around, since Smash won't be here 'til halfway through 2014.

I think the sales will pick up with game releases. There should be a string of hits with DK, Zelda and SM3DWorld and with Christmas Wii U's will sell. If Nintendo reveals these supposed unseen new experiences that they don't want copied, things could really pick up. And with a price drop and MK8 in the spring Wii U could become a big hit. It could also still be a failure, but I think Nintendo's brand is too strong for a complete failure.

gamecube sold around 20 million.....

True, but I don't want a Kart and Smash box just like my original Wii, I want a dedicated gaming system.

Look, Smash Bros, is one of my top games this generation, and the Wii U one will certainly spike console sales for a while, but it will not turn it's fortunes around at all. Melee was excellent and sold quite well, too, and yet look how the GameCube turned out.

Yeah, like this game did with the GC.

But WiiU+Smashbros IS a dedicated gaming system. You won't need to buy another game for the entire gen :P