As I am a big fan of ZFS, I tweaked FreeNAS to boot&run completely from ZFS. No UFS at all. On a single 2Gb stick, root filesystem takes 431Mb on ZFS.
Having root on ZFS brings the advantages of customization of the filesystem (rw root) without the worries of "pulling-the-plug" solved by read-only root +MD of nanobsd.
The upgrades/downgrades could be simple zfs receive or clone/rollbacks.
The web interface doesn't see the zpool but sees the snapshots in root zfs.
I suppose I have to go into some sqlite db and manually add something, since the autoimport doesn't work for active zpools.
Any ideas on how to do this?