I think the WiiU has a decent idea. I just want to take it further.
Here's the core: turn the tablet into a legitimate part of the control scheme for a game. For example, in a space flight simulator, having your tablet synced to the screen so that you could tap on any number of buttons to do a variety of tasks such as load missiles into a bay, shift shields forward, send out a repair drone, shift power to engines... I feel like you could do a lot of really fun things with a tablet since you can select things by tapping on them.
Also, after using google maps on my tablet, I want a legitimate RTS on it.