Actually with this and several other things I am going to bring up, I actually made sure there was space to do things right: there was a push to make ActivityPub "https-only"
I pushed back on that, I didn't want that requirement, and it was exactly for this reason: enabling content addressing
This isn't the only time I left a critique of ActivityPub-as-Deployed as opposed to ActivityPub-as-it-could-be: see also OCapPub, which critiques the anti-abuse tools of AP as inadequate and leading to "the nation-state'ification of the fediverse" https://gitlab.com/spritely/ocappub/blob/master/README.org
Oh, and ocaps!!!