Heh, I published a post in a similar vein just today[1]. Lately I've been thinking the way to do it is have everyone publish a (paginated) Atom feed with all their public content interactions. So each item in the feed would be something like "published this blog post", "liked this tweet", "thinks this comment was written in bad faith", etc. And "follows this person" with a link to that person's atom feed. Then if you want to build a search engine/social network/recommender system, you can get started by crawling and indexing a bunch of feeds.
I'd like to make a web app (probably on replit since it makes self-hosting dead easy) that has plugins for a bunch of other sites. so you connect to all your other accounts, and then this app imports your data and publishes it to a single feed for you.
Obviously starting audience would be programmers, but I bet it could expand to a general audience too.
[1] https://news.findka.com/p/we-need-user-centric-data