I really like the guild chat moderator new power. Also the kick+ and the fact you can only promote members up to their rank.
However, what do you exactly mean by "their own rank" how is this going to work?
To be honest I do believe there should be ONE power that allows the player to change guild news, guild interests, recruiting method and wither its opened or closed and finally the ability to create a rank with full power. This is how someone can really be called "co-leader" if he has all of those powers. Would you not agree?