Edit: I forgot about Project Trident. They migrated away from FreeBSD to Void Linux with ZFSBootMenu. They did actually support root-on-ZFS through their installer. They gave up after about 18 months, they weren't able to differentiate enough after they stopped being based on FreeBSD.
I remember the disappointment after PC-BSD died and Project Trident invested their 'time' into Void Linux instead of FreeBSD ... then I thought that it actually my be a good move - so finally some Linux would have some ZFS and ZFS Boot Environments love - especially as these people used ZFS Boot Environments on FreeBSD earlier ... and then it all died.
A lot of potential killed/lost there. First - PC-BSD introduced PBI packages - something that is today known on Linux as SNAP for example - some application packed together with libraries and dependencies in one 'package' - then for some reason they killed this idea - while Linux 'reinvented' it as SNAP (and others) and 'The World' was (and sometimes still) is fascinated by it. Sick. Same with Docker that was introduced in 2013. The so called 'World' went crazy with 'containers everywhere' ideology while FreeBSD Jails were available 13 years later since 2000. Sometimes I just got the idea that Linux people do not see any other innovations other then that happened with Linux system. Like FreeBSD Jails or Solaris Zones or IBM WPARs or HP-UX nPars never existed ...