POSIX ACLs, nee TRUSIX ACLs, are one of several ironies of the world of international standardization. Whilst the attempt to produce a formal standards document for them failed, they actually got implemented in many operating systems anyway with a fair degree of consistency. So whilst they are not de jure standardized, one can enjoy the de facto existence of tools like getfacl and setfacl across multiple operating systems today.

That said, I agree that it would be most welcome if there were fewer niches where ACLs are still wholly unavailable: OpenBSD, tmpfs filesystems on FreeBSD, and so forth.