I think this could work without bumping anyone. The largest problem with growing online communities is rate of growth, not absolute size. I think it is worth considering a system in which anyone can sign up for an account, which allows them to follow/ignore users and tags, but only allow a set percentage of them (as a function of total user base) comment and vote.
Not necessarily. I'm here just as much to read the comments of others as I am to post myself. I think I left a key part out of my first post. The idea would be to let a set percentage of new users become full users each day. So, if 200 people sign up in one day, the first 50 become full users immediately, 50 are granted full status the next day, etc. This could have a chilling effect on growth, but mk has said before that growth isn't his primary goal anyway. I think anyone who can't wait a few days isn't a good fit for this site in the first place.