Is there really a valid use case these days if you are not a hobbyist/fanboy or have existing Solaris workload compared to FreeBSD (or Linux if licensing isn't an issue)? ZFS seems quite well-supported on those.

Solaris is an actual System V, not a clone like Linux distros often are or a BSD.

It's got excellent support for compiling software written for different UNIX systems.

It does a lot of things with commands that other systems do with config files.

But no, there really aren't any compelling reasons why a non-hobbyist would be interested. If Oracle had continued development on OpenSolaris then yes, but they have little interest in their own version of Solaris.

Not that I'd really use it, but the integration of ZFS with the package manager on the one side and things like NFS on the other side made it really nice to use.

If a package update failed for whatever reason one could simply revert to a previous boot environment and configuring permissions on NFS exports worked directly integrated with ZFS. Really nice.

On other platforms there is a lot more fiddling around required.

I run a fileserver with ZFS + NFS since 2012 (I just checked the date) in my homelab and I'm happy about it. I could do the same on Linux of course but a little more OS diversity is not a bad thing!