Reminds me of the September problem in usenet. My attempt at a solution is to keep it in request-access beta and do targeted advertising only at people who sha

Reminds me of the September problem in usenet. My attempt at a solution is to keep it in request-access beta and do targeted advertising only at people who share interests with high-quality subset(s) of discussion on the site, so the new users usually see and can learn what high quality discussion looks like on the site even if all areas aren't mature. As the site matures you can naturally let more people in until a quite open beta, then full release trying to never take on more than say 10% of the daily active users in any given section/hashtag-cloud per year.