You should not be expecting a successor to Wii U until well after 2016 when Iwata has stated the QOL platform (separate from console video games) will be their new product/push.
That said, you should be cautious about picking up Wii U over other consoles because it will have very slow release of new quality games (generally only 1st/2nd party exclusives from Nintendo itself every 6 months or so).