A few weeks ago I read the ActivityPub specification and found out, to my surprise, that it was entirely push-based -- unlike RSS, a publishing server has to keep track of all the subscribers (or at the very least each subscribing instance) and notify each one of them individually every time there's a new post. I'm still reeling, but my immediate takeaway from this was:

1. WTF, no wonder instances have so much trouble scaling. Up until this point I'd assumed it was just due to media attachments.

2. This almost completely eliminated any interest I had in writing my own experimental ActivityPub implementation to play around with. There's a much higher barrier to entry if your toy project has to do stuff like keep a subscriber list in a database somewhere.

Alternate timeline where instead of Google taking over email, ISPs started offering federated search.