Here's an interesting update. The Wii U's latest firmware update allows for off-screen play for all Wii games (including Wii VC and WiiWare titles).
This update does come with a catch, though: You still need to use the WiiMote in order to play any game on the GamePad. This makes sense for titles like The Legend of Zelda: Skyward Sword that rely heavily on motion controls, as mapping the controls to the GamePad would have been nigh impossible, but it's a bit more baffling to have to use the WiiMote with games that have Classic Controller support. However, the GamePad does have a sensor bar built in to pick up the WiiMote's movements, so you don't have to worry about figuring out how to balance a bar on the GamePad.
Will you use this new Wii U feature?