I've considered that, as well. I enjoy Mastodon, and am working on another ActivityPub project. But in a lot of ways it's not a significant advantage over Usenet.
Mail over UUCP and Usenet over UUCP are optimized for short(-ish) messages, and deal with packet loss, dynamic IP addresses on remote connections, partial transfers, and synchronization scheduling as part of their implementation.
It would seem to be a good base to build something like ActivityPub on top of.