I feel like this is what Automattic is doing with the WordPress.com Reader and Tumblr. The proposed indieweb version is Microsub https://indieweb.org/Microsub, of which there are some working examples.
https://twitter.com/cr0ybot/status/1536089688695574529 by cory hughart .comcory hughart .com (Twitter)

In all honesty, I’d rather have something that lets me subscribe to other WordPress sites within the backend and creates a distributed social network instead of constantly chasing the social media flavor of the week. I really think @mor10 is onto something though. https://twitter.com/mor10/status/1535680258019500032