I think you are overlooking the gossip model, where people can self-host small personal relays on a tiny VPS or a raspberry pi in their closet, and all these people can follow each other and nobody needs to moderate content (but they do need to filter incoming spam, just like with email). Relays don't need to be costly services. Certainly people who aren't comfortable hosting their own relay will sign up for a service, and such services can monetize, just as email providers do today. Client development costs are limited over time; we have quite functional clients already.