@evan @finner https://www.w3.org/TR/activitypub/ says nothing about the `replies` collection, and even if it did, there is not currently a good way to follow a collection (or to do so recursively for such replies collections). The closest we have in-spec is inbox forwarding (which sadly doesn't get implemented by most fedi softwares!) but there's still the issue in maintaining a consistent and complete audience for who should get which notifications (and how to add or remove yourself to such audiences).