Reddit needs to figure out how to create more subreddits without having to overcome critical mass every single time. I'm sure I'm kicking in an open door here, and I believe I read that they were working on it already, but I haven't seen a real solution so far. The recommendations system theoretically makes it feasible for all articles to go on one big reddit even with a large and diverse user base, but in practice, they're still suffering from a situation where new subreddits are hard to get off the ground while the main page has to be shared by different subcommunities with different interests.