Two things are inevitable -- that North Korea will over time improve their intercontinental delivery systems, and miniaturize their nuclear warhead designs. Fortunately these are only low yield fission devices; that's not a distinction anyone seems to make on /r/worldnews or other subreddits, but a fusion weapon could come along later. EMP however could be a much more substantial risk.

I do wonder to what extend the US military and national security establishment will tolerate this threat to the mainland United States. There will come a point when North Korea has these weapons that they achieve deterrence, and that while a coordinated strike on the country is possible now, that possibility will be taken off the table in 10 or 20 years. Also North Korea may never use the weapons but they could easily get into the business of selling these intercontinental weapons to rogue groups. I'm seeing a strike on North Korea looming, but I see a very limited risk to South Korea; those subs like to bring out the argument of vast NK artillery forces being focused on Seoul, but the military infrastructure on Google Earth north of the DMZ is not very substantial and I suspect ROK-US forces could take all the sites out in one fast strike.