Imagine a zfs dataset (pool/mydata) with nested datasets (pool/mydata/subdataNNN). At present one can "snapshot -r pool/mydata" and it'l also snapshot all nested datasets, and I imagine most users with nested datasets would do this. But to check if anything has changed between snapshots, one cannot do "zfs diff -r pool/mydata". The option is missing. One has to diff each sub-dataset individually, which isn't intuitive or helpful. Could -r be added to zfs diff?
You should raise this at https://github.com/openzfs/zfs
Closing the issue because FreeBSD is the wrong place to implement new ZFS features.