You could start by editing this post, just add a few informations about how the server quality is important and show a few examples of the main issues you (devs) don't want to see on the masterserver. The thread I linked is probably one of the things a new server owner reads. Until this thread and IIRC, nothing on this forum was speaking about this issue, just writing it somewhere would be a good start.
About what said Lucas, such a change could be used to filter all the servers and also to allow more freedom to AC moders, let's just try to imagine something simple, when you join the multiplayer, you have the choice between the moderated servers (with official or validated maps that fit with AC goals | official game modes) and custom servers (with unofficial game modes and maps that does not fit with AC general environment like gema's maps etc). You now just have to select some "trusted" players to validate or not if a new map goes well with AC's goal.
Of course it's just an idea but maybe it's worth thinking a bit about it.
About what said Lucas, such a change could be used to filter all the servers and also to allow more freedom to AC moders, let's just try to imagine something simple, when you join the multiplayer, you have the choice between the moderated servers (with official or validated maps that fit with AC goals | official game modes) and custom servers (with unofficial game modes and maps that does not fit with AC general environment like gema's maps etc). You now just have to select some "trusted" players to validate or not if a new map goes well with AC's goal.
Of course it's just an idea but maybe it's worth thinking a bit about it.