This is a really cool idea. My only gripe is that Win32 is necessarily built on x86. AArch64/ARM is up and coming, and other architectures may arise in the future.
Perhaps that could be mitigated if someone could come up with an awesome OSS machine code translation layer like Apple's Rosetta.
Not sure on Windows but with Wine you can totally use Win32 on arm.
There's not much x86 specific about Win32 and you can make native ARM Windows programs for years already. WinNT was designed to be portable from the start. Windows/ARM comes with a Rosetta like system and can run Intel binaries out of the box.