Better to put it in a container ship with lead shielding to hide it and drive that ship into a harbour as a normal trade vessel. Much more effective on all counts, 20000x cheaper than a missile program and much less risk of the enemy shooting down your delivery vehicle. The North Korean Missile Program is more of a hedge against sanctions, a marker to be traded for access to the international banking system and famine relief than a weapon system. My guess is that shit is getting very dark and they are getting desperate for relief.
When you grow up in Los Alamos, NM and have been visiting replicas of Fat Man and Little Boy every year or so since you were born, your social studies classes tend to be a little different than the norm. You play peculiar games where students are assigned to ten countries and each country is given a supply of zero to ten nuclear weapons. You play the Ultimatum Game in 6th grade. And you study policy nearly as much as you study history. The big mistake Joe Average makes about nuclear weapons is assuming they're weapons. They aren't. They're policy tools. I think it was one of Rafsanjani's lieutenants who, when asked in 2006, why Iran was developing nuclear weapons said (paraphrasing) "there were three countries mentioned in Bush's Axis of Evil speech: Iraq, North Korea and us. Iraq is gone. North Korea has nukes. Wouldn't you develop nuclear weapons?" If North Korea wanted to blow us up they would have done it a decade ago. If Russia wanted to wipe us out with bioterror they could have done it four decades ago. Countries mostly want to do what they do without anybody else interfering and WMD is a powerful disincentive for the Big Boys on the Block from coming and fucking with your shit. If North Korea were in Africa, and had no nukes, we would have invaded in the '70s.
Case in point? India and Pakistan. There has not been an open shooting war there since they both went nuclear. India is pushing its space program for the same reason that the US and USSR did: take the satellite off the rocket, put a nuke on it and now you can project "Don't fuck with me" across half the globe. NK sees Trump as weak and distracted, my guess. The tests are to remind the world that they exist, and to drag the big powers to the table to extract concessions on food and fuel, like they have done for decades. As you have pointed out here previously, nobody wants North Korea. The South does not want to take the place over an integrate 25 million starving illiterate brainwashed peasants. China does not want to deal with them, and wants them so the US does not have bases on its border after the South takes over. So we get this rouge state that is allowed a limbo status because it existing is the better of the other options.
I added this to my reading list this morning. It's 61 pages of RAND - which tends to be a little dry - but the basic argument seems to be that we could fold North Korea down so long as we took care of the nomenklatura and made sure they had: 1) safety from reprisal by the proletariat 2) secure socioeconomic position in any new regime 3) improvement of the lot of their nation Basically, if we can make it better for the country without fucking over the intelligentsia we could probably get away with it. They use the reunification of Germany as their exemplar and the collapse of Baathist Iraq as their reason not to try otherwise. I think North Korea is pursuing a nuclear weapons and missile program because it's the quickest way they have to the Big Boy Club. They're basically looking for the pain point where we're willing to give 'em amnesty for six decades of fuckery.