Could a messenger like Telegram or Signal be created on top of AP? Could such implementation replace all the numerous messaging apps I currently have?
I think it should be possible. For example, federation in Plemora seems lightning fast on a local instance. (Mastodon is a bit heavier and slower it seems. Then again, I’m currently fighting interop issues with Plemora instances.)
So it seems it should be possible to build a decently responsive messenger with ActivityPub.