Wii U does run PowerPC, normal Windows is x86 only (yes and there's a arm version).
There's no way of emulation Win XP like DosBox since XP is based on Windows NT. (Win 9x is still DOS-based)
Virtualization would take way too much resources than a Wii U could offer.
So, while Linux might be completely possible don't try doing this as it surely won't work. And if it would work you wouldn't be satisfied by the performance.
I'd recommend you buy an older NUC like a NUC6CAYH as those are pretty cheap, run older OSes and do have a lot of performance for their price and size.