[rincebrain]

You are correct - ZFS hardcodes the assumption that data's location on disk will never change once written very deeply, and offline dedup/data migrating of any sort would require that.

(It would also be a performance nightmare - you'd have a permanent indirection table you'd need to use for _everything_, and if you've ever seen how ZFS dedup performs with its indirection table not on dedicated SSDs, you can understand why this is terrible.)