@aral @bhaugen ActivityPub, from the spec perspective, *IS NOT* everything is public. That's a common misunderstanding due to the most popular instance being a Twitter clone. But that's false. ActivityPub's origins come from trying to bring email-like private addressing (to the extent email really is private) to the fediverse, with public stuff being a special exception.
And that's not even to consider the current stuff I'm exploring in Spritely, which is taking some of that further.