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.
Can you rephrase this as;
"I'd like to see a model where I can pay a lot, and thus allow 10 other users for free" ?
How about something along the lines of "it costs $10 per useful per month to make the platform sustainable. A subscription is $100. When you subscribe you pay to keep 9 other users on a free account."
In other words, my question is, are upu in the 10% paying for everyone, or are you in the 90% getting it for free?