It’s easy to implement, it just may be hard to model and structure it in a clean orderly way, if you don’t know where some ideas will lead. I’ve refactored my current project a few times in the past year, and now I finally think I have my magnum opus, while it was fairly ugly before.
I could have actually had something years ago, back when the standard was reaching ratification, but I fell into the trap of trying to make JSON-LD the first priority. Pretty much any of the projects that just parse ActivityPub as plain JSON were the ones to actually go anywhere.