The most recently ported ZFS version in HEAD and 8-stable (which includes 8.1) is 14, and now a call for testers was issued for v15. This new version brings in user and group quotas and there is a hint toward importing the latest ZFS version.
A good thing about this patch / CFT is that ready-made minimal ISO images are provided for potential testers, which can be used to install new systems on real or virtual machines. Very convenient!
On the other hand, ZFS has gone through nearly 25 revisions in 5 years of development. There's nothing wrong with it but it indicates it's under active development and constant change - caveat emptor.