They had war games in 2010 and its airforce was a farce with crashes, collisions and WW2 bombing precision. Their forces are lots of people and little else. The chances of them doing an airburst over LA are....slim.
They may be .
But,
Missile plus EMP bomb is not impossible with DPRK's current tech. I think it might well be what they are working towards. (The relatively low yield devices demonstrated thus far seem to point towards it One "Dud" is a mistake. Consistently producing low yield nuclear explosions is actually quite tricky!)
The problem is how would (Could?) the USA respond?
Although lots of people are joking about it, a Nuclear strike on NK is completely out of the question! Any large scale conventional attack would also be politically very difficult.
"Defeating" NK conventionally would likely require killing
Millions of north Korean people! (Both civilian and military)
I really do have the feeling that DPRK has something of an advantage here!
How they are hoping to make use of it will remain to be seen!
(Very much a case of "watch this space!")