The whole point of reddit is that the crowding issue is self-correcting -- you just move to a new sub. I like to envision it as a malthusian catastrophe -- as the population starts reaching capacity limits, people start grumbling more and more.. until suddenly they far overshoot the capacity, and leave en-masse to new subs. In one fell swoop, the original sub is left near-empty, and out of the many new subs created in that instant, a few survive with healthy populations.