I see an 'Uncle Jim' model evolving for relays. Church group relays run off Church funds, Colleges will have their own relays (early BBS-internet vibes!) Perhaps companies will replace Slack groups with closed relays. Maybe hospitals and pharmacies will be connected with with relays using Vitor's Nip-82 (Medical Data over Nostr). Some others may just run them to deliver you content (and ads).

They only have your keys, so who you follow, (and your IP, if you aren't hiding that), possibly some other Metadata, including device or browser info comes through I think too. Still, your follows and likes is a good place to start ad-wise.

Of course, the main incentive we have for running relays is... getting paid. Now, Nostr will be a great way to orange pill. However, if you aren't already orange-pilled, there may be some more normie-friendly apps, such as Damus that will offer relay service for fiat-card payment through the app store. However, Lightning is the way I expect most relay operators to be paid. There are a bunch of paid relays, generally around 5,000-100,000sats, basically all one-time payment.

One time. Forever? For a year? No terms, no contract. Clearly this doesn't pay the bills forever, it just keeps out bots/spammers. So, they need to make some terms, and start to experiment with different plans. (Of course bolt12 reoccurring payments would be really nice right now.)

Paying per post probably makes the most sense IF it didn't have the friction. What if you could at any time load the relay with sats and the balance just automatically adjusted down say, 40 sats every post. You could check your balance at a website, or by nostr-DMing a bot.

Of course, the market will decide in two ways: -by users choosing relays they prefer

-by relay operators finding sustainable business models causing them to continue actually run their relays, instead of just getting frustrated and saying to hell with it.