Look, I hope as much as the next guy that this is all bluster. In fact, I suspect this particular round of noise is actually aimed at China, which for the first time has co-sponsored sanctions. They've clearly put NK's nose out of joint, since the Chinese are the only ones who can really make sanctions bite. Worse for the NKs is the fact China has now made clear to the DPRK that they, the Chinese, see the issue as multilateral, even though NK has always wanted to play the bilateral game with the US. The Chinese have therefore also made clear it is no longer content to allpw NK to go round and round on the "we make threats and the US gives us free s*** ride.
My fear is that the DPRK leadership, whoever that is, is in fact irrational, a bunch of genuine, fratricidal nutbars who actually believe their own BS. Worse, they may actually think that, no longer able to gouge free s*** from the US, hey may try to gouge it out of China by triggering real-live hostilities across the DMZ.
If things really do kick off, they've got a lot of good old fashioned "point and shout bang!" delivery systems not far from Seoul. Enough to make a hell of a mess.