I am betting the farm on one of two things, or both combined.
Supplemental Computing Device (SCD)
Perhaps theyve perfected it and then it makes complete sense to sell a system as weak as Xbone for 199 because you can give gamers the options of enhancing their own experience by as much as they want. Perhaps using PC like settings to determine the fidelity of your game based on what kind of SCD youre using. Then all the rumors would make sense. Even the handheld could possibly offset some physics/AI and other things to servers/ PnP as they stated, Id imagine having fully animated, semi interactive sky boxes with hundreds of things going on, or a really intricate night time or day time sky, more intricate weather systems etc.
Thatd be a real revolution and it could work for both. Could be why some leaks have said its pretty impressive, and others have said not so much.
This one is a bit more out there but:
Advanced AR
Some kind of advance in AR in a way which makes it affordable and fun, like NX mobile platform comes with glasses which give you an augmented view. I imagine playing pokemon and actually seeing the pokemon in real life battle would be pretty amazing. Or Yugioh or something and having an actual card battle, but a Magic: the Gathering game where you see the battle taking place in real time. Maybe even allow people with said AR glasses or NX portable to also watch these battles, then it can bring back table top gaming/social interaction in a huge way, which we know Nintendo is keen on. And for the console AR glasses could do something as simple as display communication chatter or something or a small hud which comes up if you glance at it, or any number of things.
Its something which could also work outside of just gaming, like a google glasses done right, in a more mainstream, simple direction ala Nintendo.