Even today, a pc that is more powerful than a ps4 can hardly emulate a ps3 or a xbox 360
Wii U, well, there are way higher probability that it gets an emulator before ps4 or xbox one since its specs are very low... for a last gen console
Today, no, it won't be possible at all to play wii u on pc (unless you like when there is less than 1 fps).
In 4 years, yes, it will be possible, with the kind of specs that will be available then :
1TB of RAM
3PB of HDD (1 PB = 1024 TB)
12,4 GHz Intel processor
Processor of 34 core
Graphics card : Nvidia GTX Titan Ultra next gen with 48GB of VRAM
Monitor resolution : 64K
DirectX 14.2
And I'm talking about a common pc, not about a gamer PC
Lawl wat? No. The Wii U is hardly anything more than just an upgraded Wii. It literally has all the same hardware. No need for this 1TB of ram, 12.4 GHz processor shenanigans. To give a reference, my Mac Air can emulate both Wii and Gamecube games just fine, with these specs:
1.3 GHz Intel Core i5
8 GB 1600 MHz DDR3
Intel HD Graphics 5000 1536 MB
HDD doesn't matter. You just need enough space to store the backups, for Wii U that's anywhere up to 25GB per game (for the largest). Wii U games fit on the internal drive, and are expected to have multiple on there (it's only a 32GB drive). My largest Wii U download is DKTF, which is about 10GB. So no. A "3PB HDD" is not needed at all. A regular HDD would work fine. Though, I'd recommend a 500gb or so, if you plan on keeping all your games on there. Anything you'd use for your Wii U would work.
"Cores" in processor don't matter. You simply need as many as the console your are emulating, and perhaps one more to keep the computer running smooth and to do extra emulation stuff. Again, any modern gaming desktop should be able to handle this (a 1.3 GHZ, dual core runs fine for Wii).
Monitor Resolution is hilarious. Since your display literally doesn't matter in terms of emulation. And "64K" is laughable. Modern displays are just barely reaching 4K/5K. Which is /more than enough/ for displaying an emulated Wii U. Really, you just need 720P, like your TV (which is perfectly capable of displaying Wii U games). Computer monitors blow past this spec requirement.
And "DirectX" isn't used in emulation, like ever. IIRC Dolphin used it at one point, but it was slow and buggy so they ditched it for OpenGL. There's no hard requirement on the graphics library, since literally anything would work. That's not a computer spec anyway.
I'm fairly certain any top of the line ($800-$1000 custom built) modern gaming computer would be able to run Wii U games just fine. No need to play with "fantasy specs". The machines we currently have are more than capable. The Wii U is underpowered as shit, which is why it's so cheap (you can pick one up for $200, and most of that goes to the gamepad).
Now, if you want to emulate the PS4 or Xbox One, that's a different question entirely. Those are built to be equivalent of a last generation top of the line PC. Which are much more demanding. Should still be possible. But I'd give it a year or two after the consoles are 'dead' in order to have the 'perfect' specs to come out, and for a rudimentary emulator to appear. Likewise, PS3 and Xbox 360 emulators would run fine now, with modern computer hardware.
If the specs you listed truly were needed, we wouldn't even be able to emulate Wii/DS yet.