Worked in a social media startup , want to build one too. My opinion -

- High level human moderation.

- Country based communities

- Actually creating services around the community to justify a subscription to participate model. You can't build any community where people without stake in it, gets to control it.

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But this comes with the obvious problem of, this won't never work. People won't simply signup because there is so much loops to jump through to say something freely.

implement voting ring detection like on HN

Start new community around new products.