China aren't going to be happy one tiny bit with this latest threat, if anything will give the world the keys to regime change within a country, it's threatening Nuclear Armageddon. The idea of Western Troops wandering about in North Korea is the last thing China wants, and the more aggressive and psychopathic NK acts, the harder it is for China to justify non-military intervention in the face of the rest of the world.
Frankly, China would rather enforce regime change itself than have that kind of liability on its borders, it has its own National Security to think about and I wouldn't be surprised if extremely strong words are being had behind the scenes.