Well, I can tell you then what technical problems exist — paid/good relays work today cause nobody actually takes nostr seriously and it exists like echo chamber. It all ends once there are a lot of ppl to attract businesses, scammers, SEO/SMM specialists etc
Client side algos won’t work. Algo by design needs a big corpus of documents that gets processed non-stop and requires biased development of both engineers and data scientists. So its a server side thing and your phone will never handle it so its actually a type of moderation. Hopefully, somehow it will be possible to chose “algos providers” but technically its EXTREMELY challenging
Moderation is a very complex topic and it can’t be solved solely technically (again, unless all you want is to communicate with friends and family). You can start overview the most basic problems of centralized social networks here https://www.techdirt.com/2022/11/02/hey-elon-let-me-help-you-speed-run-the-content-moderation-learning-curve/ which actually don’t go away anywhere just because we use standardized API format anyone can build for