I think the most interesting opportunity here is that ATProto’s strength is that it was built for a “credible exit”, i.e, it allows users to migrate from any centralized network to a decentralized one.
IOW, it would be a lot easier to implement Fediverser on top of ATProto than of ActivityPub.
Federation is not the natural unit of organization, that’s a hill I’m ready to die on. The problem is that most people get hung up on the idea of instances because they’ve only experienced the two extremes of siloed networks and the “Dark Forest” of blockchain.