NixOS has ZFS. I don't have long-term experience (switched to NixOS only two months ago or so), but the installation is pretty simple: (1) boot he installer CD, (2) add a line to your configuration to enable ZFS support, (3) switch to the new configuration. And then you are ready to install on ZFS root. Encrypted root also works.
Ironically, I felt less of a need to use ZFS on NixOS. I don't have a large pool and snapshotting the system is not really necessary, since in NixOS you can always roll back to a non-GCed previous version on your system. But I use filesystem compression and might use snapshots on /home.
I used these instructions:
https://nixos.wiki/wiki/NixOS_on_ZFS
Ironically, I felt less of a need to use ZFS on NixOS. I don't have a large pool and snapshotting the system is not really necessary, since in NixOS you can always roll back to a non-GCed previous version on your system. But I use filesystem compression and might use snapshots on /home.