I just posted this in read me first forum in response to another poster there, but it's more appropriate here:
I always wanted a system where the king would start out at 'Pleased' relations with you, but as you grew in wealth his relations would sour and he would start demanding gold and raising taxes ("The crown wants a share of the New World's wealth" diplo penalty). Of course, if the king decided to declare war on another power and he instructed you to fight as well, you could gain a mutual struggle bonus that would permanently restore some of the king's confidence in your colony.
Basically, something more dynamic than the base system of Cautious -> Furious as you refuse his demands. I haven't gotten to play too much with the "REF" relief by acceding to the king's demands, as a disclaimer. If you think the game's diplo with the king is satisfactory with this addition, don't mind me.