@esther It's not that "everyone" waa there, but that almost any group you could define had some member there, ready to pass information either direction in the event of major happenings where it mattered.

Replicating that doesn't even need "one place"; that was just the only way to get it under a regime where platform owners actively prevent communication without joining & submitting to them. But all it needs is a shared medium people can communicate across and self-organize.