Sounds like a Vita-like mobile unit, maybe more tablet like (a decent rendition of the Wuublet might be a good idea), and Wuu like synergy with the main console. The problem with the mobile aspect is if it doesn't run Android or iOS, it's basically redundant.
I think Nintendo is way too protective of their IP to really consider making an Android phone. In a heartbeat modders&hackers would be rooting their device, exploiting their network infrastructure and pirating their games to run on other smartphones.
What I do think they could be doing - considering the shared architecture suggested before by Iwata and others - is that the Home NX and the Handheld NX both have the necessary hardware to essentially run the same game, with the difference being that the Home would run them at 900-1080p while the Handheld would do so at 600-720p without antialiasing, anisotropic filtering, lower-resolution shadows, reduced viewing distances, reduced FOV, etc.
This way the Home and Handheld NX systems could really participate in the same game without the Home having to offload processing towards the Handheld. Also, there wouldn't be any limit to using Handheld NX systems together with one Home NX in local coop mode.
This way, all the NX titles are automatically cross-buy.
Also, of course the Handheld NX has a dual screen and a size similar to the Nintendo 3DS XL and the top screen is 3D capable for backwards compatibility.
Lots of wishful thinking, though.