Of course, adapting an existing system as deployed isn't easy.
I will say though that I think if Bluesky were to become *actually decentralized* it would look a lot like ActivityPub in terms of having directed messaging. This will also introduce similar challenges around eg replies, etc.
To the end of the fediverse, perhaps I sound bitter, "they didn't adopt ActivityPub the way *I* saw it!"
The truth is that Mastodon didn't, but Mastodon also saved ActivityPub. It then painted a vision of the future that wasn't, at least, what Jessica Tallon and I expected of it. But it saved AP.