I think NX will indeed be a Fusion platform that shares many of the core Nintendo IP.
So the question that a lot of people raise to that is "well then why buy both".
Nintendo's answer to that will be that the home console version will have all types of wacky to it, as in new ways to play.
In specific I think the NX Console will be Nintendo's "answer" or take on VR ... kinda. Nintendo patented this about 8 months ago:
http://www.gameranx.com/updates/id/22968/article/nintendo-patents-a-3d-eye-tracking-device/
These is 3D head tracking, tech that's actually been around for a while, but it also incorporates things like being able to blow wind into the users face and create aromas/smells.
The reason I think Nintendo is going this route is because they've said while they're interested in VR, they don't like the "putting a giant helmet over your head and saying bye bye to world around you" aspect of it. This allows for a cheap, sorta VR experience, but since the glasses can be transparent you can play with and still be aware of your surroundings with your family/friends.
I'd expect a funky new controller to go with this (maybe a traditional type pad that breaks into two to become Wiimote like pointers/motion tracking devices).
That's basically my guess as to what NX is, but I think it could be some what spot on. I remember I largely predicted the Wiimote before its unveil, but the shape that I drew for it was pretty much exactly like the nunchaku instead of the Wiimote. But it was basically the same thing, wand type controller with pointer + motion tracking features that could emulate things like a sword or baseball bat or whatever.