In the latest Nintendo Direct stream, it was announced that the 3DS and Wii U are getting a YouTube app. Details of how the apps work were shown as it takes advantage of the two-screen system of both formats.
It started with the 3DS, showing that you will watch a video in the top screen while you can search for more in the bottom touch-screen.
The Wii U app will have an upgrade to improve the user interface , allowing you to watch videos on the gamepad and watch a video on the TV while searching on the gamepad.
All this will happen later this month, no specific date was given.