> Without having to save user generated content you can save tremendously on servers. You don't have to scale other than enough to handle the fire hose.

Or just get rid of the false binary between centralized control/data (silo model) and decentralized resource-consuming p2p apps (blockchain model).

Federation models provide a sane alternative and have proven scalable/maintainable in the long run (see email/xmpp).

For federated web protocols, see ActivityPub, Linked Data or WebSub. Outside the web, there's the old and wise XMPP.