Do you think kbin is just reaching into other servers and pulling the bytes off the disk? You can't guarantee anything is deleted in a federated system, other servers can just ignore your delete request. So this makes no difference.
And it breaks easily. I still can see several posts on my private instance that have been deleted. The delete command never made it to my server for any number of reasons. As some posts never make it to my instance either.
I guess in the long term some kind of delivery queue and guarantee would be nice.