Considering nintendo and co mentioned they are focusing more on a New Handheld than "fixing" the 3DS, It will be interesting to see what they will bring to the table.
Granted much of the technology will be to do with logistics, applying
This type of content-adaptive parallax barrier with just two or three viewpoints would prove to fully legitimize the 3D screen as a practical display.
Reducing the distance between the screens seems like a Logical idea, Heck they should just pull a PS4Vita and use a capacitive touchpad in all honesty, and make the top screen 1280*800. Of course improved controls.
The XL strategy is pretty widely regarded as the best setup at this point, so they should really just go with a thick, wide profile this time around.
A proper godDang camera-set should be a thing, and I am a firm believer in the idea of an "mostly on" 2G whispernet.
Development should definitely be streamlined, in fact it could be quite interesting to see if AMD gets their flax sorted out by 2015 and Nintendo goes the mobile x86 route. In fact that way they could roll releases into smaller cycles with games running on consistent architectures. I would be happy to have a "XL" and "upgrade" every other year.
The obvious run-on from that would be using the DS system as the "gamepad" for the future wii once they actually plan ahead with their hardware integration for once.