I think about this since you added Items and customisations to the King.
How nice would it be if the King of the attacked Castle comes out of the Castle Gate as soon as the Gate becomes the first damage?
This would be awesome because you will stand against the owner of the Castle in the last part of the Attack. Sure it should be a AI like the other defenders and without spells but still powerful because of the high HP and the other stats of the King.
This would make Customisations more meaningful and would add the Feeling that you really attack another King.