As a bit of “what-aboutery”, here’s an alternative possible hypothesis;
Kim has distanced himself and DPRK from the control of China, this for the Chinese is less that acceptable in their back yard as it reduces their comfort about both the stability of the peninsula and the certainty of a buffer from the "forces of democracy" in South Korea..
Either by accident or design, the west is now pushing China to reign in NK.
This presents China with an opportunity.
While the North Korean’s are looking south and east, China invades from the north and west … toppling the Kim dynasty and replacing it with a more agreeable regime. On the way out, in order to assure future compliance, the PLA establish a base or two including a naval presence on the Korean east coast, along the Sea of Japan, something China currently lacks.
What does China gain? i) A chance to test its military capability, ii) removes a burdensome nuisance on its southern flank, iii) presents itself as helping the rest of the world, iv) believes it has stabilised the DPRK (it could even go as far as taking steps to improve the lot of the average citizen) and v) gains a strategic base or two along the way.
Not quite the Win-Win the West might have hoped for, but still, a problem removed.
JAS