Not concerned about Kim Jong Un attacking Australia.
Even if he does have viable nuclear missiles, there are a hundred far more urgent targets he would have to attack in his own neighborhood. Attacking Australia would take too long, risk of failure far too high. It would be easier to do it using a spy with a suitcase-bomb, and that would be not only difficult but also pointless in terms of North Korea's interests. He might as well attack Poland or Argentina... I mean, he doesn't really have any fans, except China (sort of).
The Kim Jong regime is basically a nervous terrorist in the corner of the world stage, brandishing a bomb and shouting "don't come close or I'll pull the trigger!!". If they ever do pull the trigger, it's game over for them, and the only small comfort they get is that innocent people had to die in order to take them down.
Kim Jong Un doesn't want that, he wants to continue being a despot, living the high life at the expense of his frightened oppressed population... who are effectively hostages.