The primary ways to monetize/support a social network:
1. ads (sponsors)
2. paid features / subscriptions
3. selling users' data
4. donations
You forgot about the attention economy? You simply let advertisers buy the attention directly from the users. Synereo has a good business model, as does GetGems.
You can't use the ad model on decentralized platforms without violating people's intellectual property rights, specifically their attention is their property.
So the way to monetize it is to build enough of a network effect that advertisers will want to access the attention of the users, then pay the users in your UIA when they watch ads. Pre-allocate the UIA to pay for your own development.
These are good points, but imo still fall into "ads" category. There's definitely a lot of room for creativity there... for example, paying users to re-post advertisements, allowing users to promote their own posts, etc.
When it comes paying users to watch or click ads, it's very hard to defend against fraud. Google has been in an uphill battle against click fraud botnets for years. It's doable but gets complex when you account for all the ways to game such a system.
I don't think anyone has tried to create an open-source ad-free social network driven by micropayments, have they? That's something I'd like to see..