This is personally how I would design the NX, not saying this is what Nintendo will do though.
Make a new version of the Wii U chip. Dump the IBM cores with newer 14/16nm AMD CPU cores that can mimic/emulate the PowerPC cores. Die shrink the GPU to 14/16nm. Maybe strip the eDRAM and replace with 32MB of HBM2 RAM if its cheaper/more power efficient.
There's your mobile NX chip for the portable at 7-8 watts. Can run Wii U ports easily, and by "absorbing" the Wii U chip, it should be able to run Wii and GCN ports and all VC stuff easily too. Mobile can run Android apps too.
Console, I'd take the cheap redesigned Wii U chip mentioned above and marry it to modern off-the-shelf AMD PC parts. Zen CPU + mid-range Arctic Islands 14/16nm GPU (2.5 TFLOP?). 8GB HBM2 RAM. Very, very easy to port PC games to, in fact I'd make the console dev environment tailored towards allowed for easy porting of Windows PC games so much so that developers don't even have to really make a seperate NX version, they can take their existing PC game and fine tune for the NX very, very quickly.
So the home console can run basically PC ports + has that redesigned Wii U chip so it can run all the portable NX games (at higher res) + handle easy Wii U ports + VC stuff + Android apps.
So that's a setup that basically works for every developer. If you're a Japanese studio and making a portable game that's also playable on portable is appealling to you, well just make the game primarily around the new Wii U-type chip, then on the console version you can simply just use all that extra horsepower to bump it up to 1080P/60 fps/8x AA or maybe even 2K/4K resolution for the NX console.
If you're a high end Western dev this works, as you can easily adapt your PC games and ignore that propietary Wii U type chip if you want. If you're a low end Western dev this works, because you can easily port your Android apps.
