I agree with shminux that keeping Main as a section one can post to is useless. I would have as places where one can post: 1) Theoretical rationality, 2) Applied rationality, 3) The Future, 4) Meetups, 5) Misc.

Then make it that ordinary posts above a certain high karma threshold (e.g. +20 or +30) get automatically Promoted to the front page, in addition to community-important things like a periodic list of meetups and, possibly, other posts at the discretion of the mods. Having Main as a separate section only causes this pointless self-callibration game in which people have to evaluate whether their posts are good enough for it, often failing and requiring posts to be moved from Main to Discussion or vice-versa.