EDIT. Yep. You are right.
From what the OP said. It doesn't sounds like NX is going to be a powerhouse. I doubt it will have the power to emulate WiiU.
Sorry, but I'll have to disagree. People using Cemu, which is being developed purely by reverse engineering the Wii U, are getting almost full speed emulation on some games (Mario Maker) with low-specced PCs. With all the documentation available, i'm quite sure Nintendo devs are able to code a competent enough emulator.
PPC is a well understood architecture and not that dificult to emulate (see Xbox One BC, or Dolphin. Heck, PearPC will turn 12 yrs old next month). And the Wii U GPU is not some unknown part using bizarre instructions.
Also, for the people concerned that by going the x86 route for the console and ARM for the handheld, the whole unified architecture idea goes to toilet, that is not the case. Almost nobody (except Middleware developers) code to the metal anymore. Just look at the Android, iOS / OS X or Windows ecosystems for good examples on how to handle multiple architectures without much trouble. For a pratical example, most of the apps on the Play Store (coded to the SDK) can run on ARM and x86 phones.