Two BSDs (NetBSD and FreeBSD, no OpenBSD, don't know about Dragonfly), and a handful of Illumos distros (who call the feature LX-branded zones).
> If anything, we should be taking about Linux compliance.
Please no; a standard defined by one implementation isn't a standard.
Linux has another implementation: WSL 1
As for your second point, it just means that package management is irrelevant to UNIX (or POSIX) compliance. It did not prevent different package managers to appear over the years, because all the expected infrastructure was in place.
But did these UNIX package managers actually materialize? I guess my point is: is UNIX at all relevant? It had some really good ideas that were worth copying, but the world has moved on to greater ideas.
Obviously yes. I don't understand what is there so hard to understand.
I mean, just go learn about pretty much any field where you need to target a combination of platforms that don't agree on small arbitrary things, and how much wasted effort that consumes.
You've assumed that your perspective is the correct one without justifying it. Sure, standards are important, but UNIX doesn't seem to be a successful (or modern) one.
If you're interested in learning about why standards are "such a big deal" then you can start by discovering a phenomenon called linux fragmentation".
UNIX covers exactly zero of those. If UNIX was worthwhile, we wouldn't have Linux fragmentation or, indeed, an article explaining how to run UNIX scripts on a UNIX-compliant OS (sure as shit ain't a standard if it doesn't actually work).
I don't understand why UNIX is such a big deal in 2020. Linux has won, and at least one BSD has binary compatability with Linux. If anything, we should be taking about Linux compliance.
Having no strong package manager story, yet being UNIX compliant, seems like an extremely bizarre priority choice.