I agree. It's hard to imagine an open protocol that can't be normally used without paying. In my opinion, the classic social media monetization model through advertising (but without collecting and trading personal user data) could bring popular free relays into profit. Which in turn could share the profit with the developers of clients promoting these relays by default. And if user don't want to see ads, there always will be a free relays without ads from ideological altruists or ability to connect to a paid one.