The thing with his underground testing is we don't know anything about the parameters of the weapon tested. I've been to the nuke museum, including classified parts, and the first US H-bomb would have had to have been delivered via a freighter, it was approximately the size of a large cargo container or boxcar. It took a long time and a lot of cutting-edge tech to get one down to what an aircraft could lift, and they don't make efficient missile warheads because multiple fission weapons on MIRV vehicles actually work a lot better than a single fusion weapon. His missile tech has had some extremely mixed results, missile capability that works some of the time and has a forty percent chance of getting a minimum weapon package to the end of its trajectory is a shaky way to deliver weapons that you possess in very limited numbers.
We can tell if something blew up with an underground test. We can tell about what magnitude it was. Everything else is conjecture. Unlike his first couple of tests, this one was too big to fake with a few thousand tons of conventional explosives down the hole, but the fact of the matter is we have no idea whether the weapon was small enough for any of his vehicles to lift or even close to that, and whether or not it was actually a fusion weapon or just a bigger fission weapon.
I think we all know though, time is our enemy here. Nukes are quite simple devices... but very difficult to get right. Basically, a mass simply has to EXIST in the correct form in order to "explode" with such unbelievable release.
Right now, I don't think fatboy is capable of producing more complex compression triggering systems required. Of course I'm basing this on pretty much no actual facts, just the state of the place.
I mean, they can't even produce an aircraft or turbine on their own. They almost HAVE to be buying this stuff, not developing it themselves. Mitigating those purchases isn't really a "solution" of sorts, they will always find a way to get the stuff.
It's a damned shame, but I only see one actual fix for this, and it involves destruction of the communist state, starting with NK.
The only other potential solution is to go after Chinas banks with prejudice. I don't think they really WANT to be involved in this debauchery in any way, but like it or not, they are going to have to step up... we could topple China with financial moves and they know it. They're known money launderers for fatboy, we have them dead to rights... it's just a matter of leveraging that and hoping they see there is no longer a choice. Fatboy is a threat not only to that region, but stability in a global view.