In terms of tool/system integration FreeBSD's ZFS is miles ahead of ZFSoL and this is unlikely to ever change. FreeBSD has its own userland that does not need to run anywhere else; updating it to integrate new kernel capabilities is comparatively easy. This can simply not happen for ZFSoL in the same way, since it would split this integration over a myriad of projects and then still require a distribution to make all the right choices.

With regards to OpenBSD, I think it was at the last EuroBSDCon in Stockholm during Henning's talk when he said that "ZFS was not the solution" or something to that effect. Quite rich, I thought, coming from a platform where software-mirroring and disk encryption is an either-or decision (at least was at the time).