True. Perhaps a collective vote past 2 degrees of freedom out where multiple parties need to vouch for the same person before you believe they aren't a bot. Then you're using the exponential number of people to provide diminishing weight instead of increasing likelihood of malfeasance.
I suspect a lot of people here are the ones in their circle who bring in a lot of the cool info that their friends missed out on. This still sounds like Slack.
We're talking about webs of trust aren't we? Not about chat rooms.
I'm hypothesising that any such large scale structure will be perverted by commercial interests, while having multiple Dunbar sized such structures will have a chance to be useful.