Can't you just have a website like Medium that acts as an aggregator (of RSS feeds) instead of a platform? The issue I have to whether stick with RSS feeds, which seem like it's dying, or to use ActivityPub, which doesn't seem to be developed that heavily.
I think in addition to this an aggregator, you also need a website that helps create an RSS feed for each user while simultaneously abstracting that notion away. Thanks for the pointer though :)
