I think it would be a wonderful idea, Sad that nobody has made this yet as I have seen it suggested many times. I have even tried to make my own but never got very far, not much time to work on it.
For mine anyways I planned to make a king based largely on buffs for villagers and improving morale, as well as increasing their wealth through trading. either by lowering cost of trade items or even having their own form of work bench (possibly a throne?) where they could produce deals or trades instead of objects. (required items could differ and result in gold)
I think as with real life a ruler of some form could be very helpful. people seem to misunderstand this request, but rulers don't sit around and do nothing, it could if done right prove very beneficial.