I think China's influence over NK is also widely overestimated. The fact is that NK is a cult. It's more stalinist than Stalin ever was, and the Chinese economic model is quite different today from NK. About all you can say is that both have repressive governments that dominate their citizens. NK's is communist, while China has shifted gears and become fascist. Neither is conducive to dissent from their populations.
But what does China really want? I can't imagine that they're thrilled with nuclear bombs in the hands of nuts across their shared border. Nor do they want a united Korea that is pro-western. Ideally, I think they'd prefer the current situation to be defused diplomatically, and for unification to occur on terms that would eliminate US influence.
The surprising thing is that this is what was about to happen before NK started its uranium enhancement project. The SK sunshine policy was well underway, and even Japan was taking great steps toward normal relations.
Anti-Americanism was on the rise in SK, and all this was fitting into the Chinese goals for reduced US influence, and greater Chinese influence.
But the kooks running the NK government upset all that.
Good reply BTW.