I agree - my main reason for sharing with this post in particular is because the tie-in it has with Beehaw's recent decision to, at least temporarily, defederate with .world and sh.itjust.works; I just found the framing about decentralization, esp. the fact that the Fediverse is not a monolithic entity mandating a uniformly aligned approach, useful.
On the whole, I do think either ActivityPub's protocol spec would need some kind of privacy revision, seeing as it's already been a Problem where microblogging admins have had to block access by servers dedicated to mirroring Mastodon posts which don't delete their copies after posts are deleted by the user, or the software itself, Lemmy in our case, will have to make adjustments to its implementation of federation like you said. Of course, I'm mostly just conjecturing here and I don't actually know what either of these might look like 😅
The main part of this which I problematize are the people who are sticking their necks out for Meta and suggesting instances shouldn't be quick to defederate because this is, supposedly, a good opportunity to bring federated social media into the mainstream. Yet, in my opinion, they're not making enough of the fact that, even with their open-source contributions, Meta's software manufactures discord and bigotry on a massive scale. Letting them federate with an instance opens floodgates on that and for the stealing and selling of Fediverse participants' data.