True, though to Microsoft's credit, the existence of the POSIX subsystem, even as a proof-of-concept, ensured the underlying kernel design supported the development of products like Interix, just as Windows on Alpha et al. ensured NT remained reasonably portable to future platforms like ARM, unlike say OS/2 where the only non-Intel release (for PowerPC) was basically a prerelease lacking core OS features like networking.

That's correct, I put them in the same bucket though, as SUA was also based on Interix. So I consider SUA more as a rebranding, not something completely different like WSL.