Hello,
i had this thought before i found this topic and althought your system sounds good as i read it i think it has the possabillity to be very controlled by who is selected for PB's if there is a large population on the server. so i thought i would state my idea incase it is able to inspire another idea.
my idea is that you can only buy a flag to capture a port as long as you are not a lord protector of a port already. this is asuming that the ownership of a port gives diplomatic voting rights and also asuming that the flag purcheser becomes the lord protector (as is the current model).
this would have the benifit of ensuring that even a large clan would not be able to take over all ports (without the use of alts, which i hope could be prevented in this case) it would also alow smaller clans to take and genereate "seats" possable even at a larger clans request and support in the PB, or against the larger clan just to gain some influence in the voting.
i'm sure you have probably already had thoughts along these lines but thought i should mention it just incase.
i guess my main fear with the upcoming diplo patch is the possable self declaired dictatorships of vocally large but ultimatly small clans takeing control with the abillity to bully other clans with as much influance in the game out of the diplomatic process.