I definitely think this is solvable via some basic honeypot laiden proof of work.

1. Exist for some time.

2. Vote on stuff that humans would vote for.

3. Avoiding voting on traps.

4. Comment occasionally and productively.

5. Post to a limited existing audience, and receive upvotes.

6. Post limitedly to a general audience.

7. Post generally.

It’s basic earn a reputation behavior.