I don't think the commitment phase on Area 51 takes too long, as many have suggested. I just think there's not enough to do for members that have actually committed. So here my proposal:
Open the meta site at 30% in the commitment phase so the community can start thinking about the big questions before the site has gone to beta. Anyone that commited (or suggested questions and committed) should be able to participate. That way, the community has something to do and feels involved, without losing the security of knowing there's a group of people to actually participate in the beta once it's there (not having that security is the risk of a shorter commitment phase).
I'm not sure if it should really be the meta that opens, though. It could probably be a forum-like site that's embedded within area 51 or whatever, but that's not the point. The point is keeping people involved during the long waiting period.