Hacker News Reader

Every popular website will go through Eternal September at some point: https://en.wikipedia.org/wiki/Eternal_September

The challenge is how to enforce quality despite the surge in users.

I had never heard of that but did notice the effect.

A required lurking period, maybe?

Unlikely to work. Required lurking means lack of participation and thus lack of learning.

My counter suggestion is to encode the culture you desire in to the function of the site.