Wii U is just a dud. Price cuts and Mario Kart won't "save" it, all they'll do is the same thing that happened with the GameCube -- a few weeks/months of a surge followed by a return to mediocre sales.
There's not much Nintendo can do about this now unless they have some kind of new franchise breathe new life into the platform, but even that, if they don't have that already well into development, it would likely be at least until 2016 before such a game could be made ready, and there's really no point by that time.
How many brands that really popularized themselves from the 80s are still massively relevant today? It's a tough task, I think Nintendo has just become too far outdated and too far out of touch with the modern game audience. Wii was just a one shot surge that really masked what was a 15-year decline for them in the home console business.
