Awesome! When the great split first occurred, I was really concerned that the Illumos path would die on the vine. Especially after Nexenta started hiring up everyone they could and not really seeming to attempt to give code back. Having been a huge Sun fan when they finally opened Solaris, and then dreading the Oracle acquisition, it's awesome to see major features continuing to make it back into the open source version of ZFS.
This is great news for people like rsync.net, anyone using zetaback, or people using znapzend. I suspect cloud storage via ZFS will see the most benefit, as they'll be sending full datasets over lower bandwidth links. The zfs backup solutions will have less benefit (except with restores) as most backups end up being incremental.
IS this going to be integrated into ZoL?
ZoL is OpenZFS, so you'd expect a future release of ZoL to include this feature.