You just have to design so the bot's aren't relevant. The problem with Twitter, Facebook, and friends, is that they push the bot content at you, even if you don't follow them.
Require a fee to post.
Similar to quadratic voting https://en.wikipedia.org/wiki/Quadratic_voting
So the fee isn't a one-time fee, but an "open" fee that keeps increasing.
Another mechanism is to require a fee to view. If after viewing the content the user deems the content isn't valuable, they flag it in some way or they don't bookmark it, and this indicates the poster should pay the display fee.
I still don't think it would work now though. People don't trust social networks like they trusted Facebook in the olden days, and they never will again.