Professional communities with invite-only registration, where invites are only distributed to people with high ratings. Also you can add higher barriers, like a requirement to write a valuable on-topic to get rating above a certain level, regardless of the comment rating level. Basically a self-moderated narrowly focused community with invite only registration.
The active user base is trending slightly downward as a few instances have shut down recently but the amount of registered users is steadily increasing so those trends will reverse as the largest barrier to entry is just knowing about Lemmy and creating an account.
It was called newspaper back in the day. Printing something was expensive so quality must have been good, that people were willing to read it. And social part was provided by posting letter to the newspaper adress with a hope to be printed.
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