A chip that runs the Unreal Engine 4 engine properly (not just barely) along with that expensive controller is going to be hard for Nintendo to sell at $299.99, if not impossible unless they are willing to take a loss on the hardware. Which I doubt they are willing to do. The 3DS was one-time bailout, it's not something Nintendo is going to get in the habit of.
Throw an expansion slot on the bottom of the system (the NES, SNES, GCN all had one) which allows for a new processor to be added later (Crossfire style, AMD knows all about this).
Then come 2014 when devs are actually making games on the UE4, a 2.5 TFLOP processor on a 28nm manufacturing process will be easy to Nintendo to obtain for $60-$70 cost and will run cool and power efficent. Bundle it with a game or demo for $89.99 and voila -- future proof console.
Same concept as Wii Motion Plus ... Nintendo wanted that tech in the Wiimote from the start, but it was too expensive when the Wii launched.
It's not perfect, but you're not getting a chip that can run the UE4 engine properly (who cares if it can just barely run it with major compromises ... everyone then is going to buy the 720/PS4 versions anyway) today in a Wii U.