Not sure if anyone has suggested this already, and while I know the Co-GM abilities are probably a way down the works, but would it ever be possible for the GM to be able to select which posts the Co-GM is actually able to Co-Edit as opposed to just the default first post? Say in the situation the GM makes an announcement later in the thread, or if there's a couple of reference posts at the beginning as can happen with RPs involving well developed worlds. 

I figure the easiest way to do this (based on my limited knowledge of coding) would be some sort of toggle option for the thread creator to enable or disable the Co-GM's ability to edit their posts. Not sure how this would work in the Co-GM made a post however as this would obviously need to be a two way street so to speak.