I think I need a little more than a TL;DR, and less than an in-depth analysis on the ongoing situation (North Korea's actions v/v South Korea's politics).
I understand why North Korean-connected actors (factions? individuals?) would happily take advantage of such a situation, but if they weren't already there (playing the long game), how?
Also, even if they're already there, manipulating what they can, I am having a tough time imagining how N. Korean-connected entities (even including the ones unwittingly connected to N. Korea), could gain a foothold great enough to affect S. Korean politics to this degree.