Soundwave on 05 February 2013
The N64 was basically turned into a portable (the iQue for the Chinese market), the chipset was able be shrunk so small it fit into an N64 controller.
If they can do with the Wii U tablet ... well there's your screen.
Still you're probably talking 3+ years out when they can shrink the CPU + GPU and manufature it on a 20nm process (or smaller).
They would need to get power consumption with a 6-7 inch screen to be in the 15-16 watt range or less. Dropping the disc drive obviously helps, and shrinking the chip does too, but I believe the eDRAM on the Wii U GPU may be the biggest hurdle in shrinking the chip.
