Without an explicitly capped profit, I can't see how this doesn't eventually lead to exploitation of the users.
I would like to see a donation/optional subscription model with tiered features as is seen in Patreon/Kickstarter etc. with the distinction that the tiers are community wide instead of being bound to the individuals donating.
Display an income bar. If it drops to zero the servers turn off. If it drops below 1 nobody can post. If it is above 1 you have Direct messaging, above 2 you have more features, etc. Keep the communication clear as to what is being provided and how it is being paid for.
Most people won't pay, but if nobody pays there is no service. Its survival would depend upon providing a service that satisfies enough people to sustain the support. This certainly wouldn't be as lucrative as a exploit the users model, but the idea is not to make a fortune, but to simply run a sustainable enterprise.
Capped profit is interesting since it doesn't limit the business model, just the likelihood of enshitification.