Wii U uses a fairly standard AMD GPU, it's a safe bet that NX will do to if it's a home console.
An AMD Jaguar core is already more powerful than what's in Wii U, IMO 3 of those clocked at the same speed as Wii U's 1.24Ghz would be more than ample.
If NX uses an 8 Core 2.4Ghz Puma or Excavator CPU, along with a GPU around PS4 or higher level then the NX home console could more than likely emulate multiple Wii U's all at once.
Wii U's CPU is certainly nothing to write home about, it's a triple core, 3 thread unit, clocked at 1.24GHz, while it uses newer architecture than Xbox 360's triple core, 6 thread 3.2Ghz unit it's still not as capable as that chip.
XB1 has no problems in emulating 360's CPU, that's using a modern Jaguar 8 Core, 8 Thread unit clocked at 1.75Ghz.
A 28nm or smaller modern AMD mobile CPU architecture like Jaguar, with a few cores locked at PS4 speeds could probably handle the job.
The only issue is that RISC program language needs to be translated to CISC, which is pretty simple, AMD could probably include both RISC and CISC recognition into the chip's design if Nintendo wants.
There's really nothing complicated about emulating Wii U.
