Never having been king, I don't know exactly what comes with it other than the boosts, but King sets rules for the server to follow. Often times, people don't follow those rules, and from an outsiders perspective, they have no recourse to correct that. I think you should give the King the ability to port people who break the rules to a random server. Maybe limit it to 5 times so the King doesn't just abuse the power though.

Either that or give the King the ability to break truce agreements to ensure that those who break server rules can be dealt with accordingly.