Having something like circles from the Google+ days would be needed if ATProto is going to go anywhere. Is it possible in the protocol?

Yeah having the messages be e2ee by default and then extending it out to one or more groups depending in which circles are currently included for messages could let atproto act like an encrypted group chat with crisscrossing group chats per message, which can ratchet up and along with the new enceyption keys each message/batch of 10 messages/hour/day until that client is dropped from a group or a group is dropped from a conversation, then the keys change and pfs prevents old clients from continuing to read future messages.

Sure you can see that users emit messages in the pds but you dint know if its for your former group or other activitt