Emulation of the WiiU on the NX would be relatively trivial as the Wii U's hardware is relatively poor.

The PC emulates things far differently than how the Xbox One does emulation, the PC will "Brute force" it's way through as it will take an instruction, translate it  and often chop it into several other instructions to be executed on the host machine, which is why it requires orders-of-magnitude greater levels of hardware.

What Microsoft has done on the Xbox One is virtualised the Xbox 360's OS, created an API between the Xbox One's hardware and the VM layer and then repackaged the games, it has stupidly low overheads and fantastic accuracy, impossible to do on the PC without intimate knowledge of the hardware.
Before the Xbox One's release, people laughed at me on these forums when I said emulation was entirely possible on next gen and they pointed towards PS2 emulation as the example of the hardware required to achieve it, even after I provided a detailed analysis that says otherwise. (Obviously I got the last laugh, when Microsoft announced it. Suckers.)

The PS3 could also be emulated on the PS4.

But that is a Software approach.

If Nintendo opts for the Hardware method... Then all they will need is probably the CPU.
And if we shrink the CPU from 45nm down to a MODERN 14nm included in the SoC, then you are looking at an insignificant cost, we are probably talking cents here as the Wii U's CPU is only 50~ to 150~ Million transisters.
The Xbox One and Playstation 4 have 5~ Billion transister SoC's, with roughly 400-500 million transisters for the CPU units, the Nintendo NX could even be larger than that.
9~ Billion 28nm chips are available, 14nm would allow you to bring a 9~ Billion transister chip down to the size similar (Or smaller, depending on other factors) to that of the Xbox One or Playstation 4's SoC.

Essentially, allowing for hardware backwards compatability wouldn't be terribly expensive, the Wii U is built on an old node and was pretty conservative with it's transistor counts.


With that said... If I was in Nintendo's position, I wouldn't bother with backwards compatability with the Wii U at all.
The Wii U does not have a large games library or fanatical user base, they would be better off providing regular Wii comptability.

OVER 9000!! Gigaflops would be enough I think.

I heard the emulated Wii games on Wii U are basically all running the Wii OS.

In everyway? Main memory bandwidth is less, cpu benchmarks far less, gpu gflops may even be less if the wii u is 176 gflops even if the wii u gpu has a better feature set. Remember the wii u is on the same 45nm process and consumes far less power. Games that exist on both 360 and wii u almost always run better on 360 with often much higher frame rates. Some games are lower resolution on wii u like sonic racing transformed. Not forgetting the 360 also generates full 5.1 dolby surround sound where as wii u provides uncompressed sound data which requires less processing.

The one game that actually looks impressive on wii u, xenoblade actually has some very simplified mechanics like lack of collision detection and the developer also produced miracles on the humble wii with the original xenoblade game.

I have ps3, 360 and wii u and for technical accomplishment both ps3 and 360 easily beat wii u. I.e. their technically most advanced games are more impressive than wii u's.

Since the wii u was released the reality of the spec has slowly been realised and its been a downhill journey all the way. From what was something competitive with ps4 and xbone we are now at an understanding that it generally performs below ps3 and 360 on average. Most of  us realised I think at the beginning just how bad it was when almost every game was sub ps3/360 performance. It was always a ridiculously poor console sold at a hugely inflated price just like the wii before it.

Nintendo looking more far then People think.. I sure wiiu just need 26 watts Because it Has been from the outset to become the mobile part of the NX... PowerPC wiiu is know for being not very powerfull... And don't forget wiiu OS run on ARM...

I don't think Nintendo looking for compatibilité but for easy port wiiu games 

I don't even think what the Xbox One is doing is pure emulation to achieve backwards compatibility. I suspect that their straight up modifying binaries to achieve backwards compatibility since they need permission to change the source code ... 

That been said I think Nintendo could emulate the WII U if the CPU has comparable IPC to sandy bridge at moderate clocks ? Emulating the GPU is easier than I thought it would be since Cemu is getting by just fine with OpenGL 4 compared to other 7th gen emulators needing DX12/Vulkan but I guess Nintendo doesn't mess around a whole lot on a lower level compared to MS and Sony obsessing over a lot of the intricate details ...