After much thought, my guess on the NX is that it will be a hybrid console that is the real successor to 3ds but can play Wii U games at home. Think smaller clamshell gamepad with removable analogs and with more features to take advantage of new handheld games.
It would drive sales (new Nintendo handhelds usually do) and with the extra device included, being basically a smaller Wii U customers will have everything needed to play the delayed Zelda.
I doubt it will be a hybrid.
If you're going to do that, you compromise.
The portable part is less portable and the powerhouse part is less powerful.
In these days of 3ds, iPhone, iPad, etc, portable really needs to be portable. And the console should be very very powerful. Otherwise, who needs one? What's the point? Might as well AirPlay your iPad to the TV....
I doubt it's a hybrid. But it will be powerful. And the handheld(s) will be powerful too, but very portable.
Microsoft tried the hybrid route with the Surface. Tried to make it both a laptop and a tablet. The end result was a compromise that was neither excellent as a powerful laptop, nor as a Thin, power saving, portable tablet. It failed.
I like to think Nintendo pays attention to where these concepts overlap.
The Wii u is someone of a hybrid compromise itself, taking the tablet idea and trying to fit in into the controller. It failed.
So let's see a console do what consoles are supposed to do, provide a lot of power which in turn provides the basis for lots of fun.
Then let's see a powerful handheld provide lots of fun in a thin, smallish form factor with the battery life that allows that fun to be had for a long time. Both of these can be run with various implementations of the same architecture (but with different clock, chipset, ram amount, type, etc.,) to enable various versions of the same titles to launch quickly. Maybe simultaneously.