I'm not convinced by ActivityPub. A lot of people seem to think that it's cool but the documentation makes it look like it's just a schema for social media applications. It might be an obvious move to try to standardize social media platforms because they all involve roughly the same kinds of user activities. Interoperability is cool, I agree. But the ActivityPub documentation has a whiff of the old XML/"semantic web" hype about it. It's verbose, unnecessarily object-oriented, and it doesn't seem to advance any kind of new or interesting vision for the architecture of these interconnected systems.
I get that somebody probably needed to do this work of standardization. As a project it seems to lack imagination, though. There is nothing to get excited about as far as I can see. It's just a consolidation of very familiar social media functions.
Not federated yet either unfortunately. But I think one of the few fediverse projects that dogfoods ActivityPub by using the client to server protocol to communicate between frontend and api.
Follows work at least. Commenting directly on stories works, as far as I remember, but I think the main issue is that it doesn't properly create a list of inboxes that a comment is addressed to to push the messages to them.
Leaving it to last makes me worry that it won’t happen.