It might be not possible to create a generic #ActivityPub server, but nevertheless this is an interesting thought experiment that helps simplify the protocol and figure out the best way to extend it.
I've been thinking about generic servers for quite some time (because this complements my work on nomadic clients), here are my notes:
https://codeberg.org/silverpill/feps/src/branch/main/fc48/fep-fc48.md
RE: https://mastodon.social/users/eyeinthesky/statuses/116095929503245071