In the real world only a small minority even use NFSv4 and that mostly for the figleaf of encryption via (yuck!) Kerberos. As a (too) long time storage industry person, I have hard numbers on this.

AWS's EFS is mounted with NFSv4 on Linux instances. Had to fight against race conditions between clients recently (per client directory caches,) but that's a feature of NFS, not specifically v4.

But quite a lot of people in the real world use NTFS.

It's primarily a corporate-level thing, but just as Windows has a strong set of ACLs that people at home ignore, it could be the same scenario on Linux.

> How many people use ACLs?

Everyone who uses systemd. Try it yourself: do a getfacl on the files inside /var/log/journal on a system with persistent logging enabled (if it's disabled, these files will be at /run/log/journal instead).

I have used them to set up a group-readable/writable directory to ensure that all subdirectories remain so.

This is a Yogi Berra type comment. "ACLs aren't supported. Nobody uses them."

Not really. Linux supports "old" posix ACLs and chungy is complaining that it doesn't support "new" rich ACLs. My point is why bother upgrading a feature that no one uses.

I think "no one" is a fairly tall claim: They are well-used on all the operating systems that do support them.

Mind also, "old POSIX ACLs" came from a POSIX draft: they never made it into POSIX. While being an extremely simple expansion of the Unix modes, they are only ever additive and do not support fine-grained permissions that NFSv4 allows for. They're sometimes better than the standard mode bits, but they very often come up short of being useful in the real world.