Right now a large portion of Reddit is willing to jump the ship at all cost. You can't design for such events, i agree, but if you had a perfect reddit clone right now - people would flock even if there was no content. This is a digg moment. The problem is scaling up when there's demand, because people don't like lag and a half loaded tab. No one is stepping up as a Reddit successor because everyone know they have no pockets to scale to Reddit scale
The network effect comes from building actual networks. We don't need a reddit clone, we need good old-fashioned forums/bulletin boards that also interoperate via Fediverse standards. This solves the scalability issue, because individual instances would stay small, and would choose whether to accept "guest" interactions from users of other instances.