HN user
How are the user agents funded? Probably through ads.
The problem is actually how to fund the timeline publication services. But systems like Medium etc seem to work OK.
I am now spending several hundred dollars a year on content subscriptions. Plus subscriptions for Gmail, Zoom and a few other things where I have outgrown the free service. A freemium model for the timeline publication services would probably work.
There are models for this that could probably work. Tim Berners-Lee has been working on a scheme called Solid for years now.
It is important to realize that Facebook is not the first, second or even tenth of its ilk. FaceBook combines a bunch of ideas from previous systems, in particular MySpace and USENET. It is more or less the third generation of Web Social Media. There is no reason to believe there can't be a fourth.
My interest in these schemes is to provide a discussion space that is end-to-end encrypted so that the cloud service collecting the comments does not have access to the plaintext. This allows for 'Enterprise' type discussion of things such as RFPs and patent applications. I am not looking to provide a consumer service (at this stage).
The system you describe could be implemented in a reasonably straightforward fashion. Everyone posts to the timeline service of their choice and choose between a collection of user agents discovering interesting content for them to read. These aggregation services could be a paid service or advertising supported. Timeline publishing services might need a different funding model of course but bit shoveling isn't very expensive these days. Perhaps it could be bundled with video conferencing capabilities, password management or any of the systems people already pay for.
As for when the Internet/Web was not so vast. One of my claims to fame is the last person to finish surfing the Web which I did in October 1992 shortly after meeting Tim Berners-Lee. It took me an entire four days of night shifts to surf every page of every site in the CERN index.