One thought I've had is if the NX controller is again a "screen" controller, perhaps they could put a mid-range mobile chip into the controller itself, so that it could perhaps play Android apps/games and DS/3DS software?
I mean I guess what would a chip akin to an Apple A9 (vanilla one) or Snapdragon 810 cost Nintendo these days? Probably not much.
Could that be why there is no word on a portable NX?