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.
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.