Finally! This is exactly what I want for handling photos and media on my home server. We have phone's dumping their camera rolls onto the machine via Syncthing, but the easiest way to share content safely is just to make copies of the file and go "storage is cheap". But the reality has always been closer to "storage should handle deduplication" - with this feature landing that can finally be a reality.

EDIT: Not to mention, this should make ZFS best-in-class for handling container filesystems. Deduplicating all the files in the individual layers means you can pretty much dispense with awkwardly trying to maintain inheritance trees.