There are going to be several levels of control in NK.
Kim and his family at the top, it needs a major revolution to get to them.
The inner circle of government who could either get offed by Kim or by their "comrades" in order to gain favour.
The lower levels of The Party who could get...
The only way to stay on top is to be the meanest sonofabitch possible. By popping off his uncle he has clearly stated he is a man to beware of, the people and the apparatchiks now know that.