IMHO, prophecy is a a pre-requisite for kingship, as it is written in Deut. 17:15: "You shall appoint a king which The Lord, your God, has chosen..." (informal translation).
Since only The Lord is allowed to choose the king, we must have a prophet that will tell us who The Lord has chosen. Since we currently don't have an acknowledged prophet, we are not allowed to appoint a king.