The only thing that I think is a must-have with drop-in games is to have a representative from each recognized clan. What happened with this last one was that the good players got chatting with people who run established clans and now they're in the clans. That seemed like a good thing and I think that there are 2 main important things for the drop-out games:
1.) To learn how to play 'socially'
2.) To get to know some people from the CMO community.
This way, the good players will be able to get into good clans, which is only fair