The Wii U has seens its Mario Kart come and go. While it boosted sales it pretty much did squat to change the inevitable future of it being a complete failure.
Let's be realistic, Hyrule Warriors won't move consoles and by the time Zelda comes out (Which also does not really move consoles outside a few exceptions) it won't even matter. Other games like Mario party 10, Splatoon, etc. will need to ride on another game that is bigger to grab more of an audience because by themselves they won't do crap to help the Wii U.
That only leave, Super Smash bros. I do believe that Super Smash bros may be the best selling game on the system a la gamecube. However, Smash has been delayed, the Wii U has already suffered a bit too much, and it's coming out on both systems (Got a feeling the portable version will sell more.) But with how Mario kart 8 sold (which is usually the bigger franchise) Super Smash bros would have to pump out heavy advertising and have big promotions (Something Nintendo usually does not do, or puts limits on) to save the Wii u. Most people believe the Wii U will sell around 10-13 million life time. This is the game to change that around.