@FBM,
I think you've hit the nail on the head with connecting this incident to the internal politics of North Korea's leadership succession, but would only be guessing about just how it is connected.
One can assume though that either the forces of Il's son and heir or their opposition believes their interests to be enhanced by a heightened state of possible war.
Military threats and acts of aggression are the only "diplomatic" coin the North Koreans have to play with though, and in the past, demands have followed such words and actions. I wouldn't be surprised if, in the near term, there is an attempt by NK to secure food and/or fuel from the international community, and the US in particular.
I wouldn't assume that China is fully aware of, and in tacit agreement with, what it going on over there, or that they only need to snap on NK's leash to make it stop.
I have to wonder how much South Korea will take, or what the US will allow before it feels compelled to somehow directly intervene. What, of sufficent significance, can be done militarily that will not result in NK using a nuke on South Korea?
The magnitude of the possible ramifications of this incident should provide us with all the evidence we need to do what it takes to keep nukes from Iran.