[Macha]

The closest example outside Windows I can think of is the idea of "zones" in Solaris/Illumos/SmartOS. You can have a "LX branded zone" where the OS will respond to linux syscalls.

I don't know if the native solaris syscall interface is itself a zone, while Win32 is a subsystem on Windows.

[ProofByAccident]

This is a cool example, and now that you mention it docker as well seems to provide similar functionality. I guess what's striking about WSL1 then (and maybe what the author was saying) is that it's a mix between a docker container and like wine.

[pjmlp]

It is also how IBM mainframes work.