it's not but i think it needs to be done as replacement events without deleting old ones so people can see the full history
dealing with the diffs is a fools errand without a consensus so each update needs to be a full new version for this protocol, on the back end the storage can do the diffing to save space
i can see it working too... all events could be replaceable actually, if you just stop doing this racy delete events thing
i've thought about this very deeply for a very long time... diffs need consensus, you don't need to worry about that on the back end of a relay, it can diff the versions of an event, all you need is a "replaces" tag and put the event hash and the content replaces the event et voila
