I actually think chubby Kim is proving to be quite the headache for China.
If we look at the entire history of the two Koreas, it's actually very striking just how reactive Chinese strategy and policy towards NK has always been.
China was most certainly not consulted when granddaddy Kim kicked off the Korean War, he did that with Soviet backing, not Beijing's.
China entered the Keorean war largely because of the bellicose tone of a certain MacArthur, who Beijing feared would not stop at the Yalu.
Since then, almost every move China was made wrt NK has been largely reactionary.
I think that is because of a combination of a lack of strategic ambition, as well as a lack of good policy solutions.
Simply put, China has very little interest in Korea. Beijing's primary focus has always been internal rather than external, with Taiwan about as far as Chinese interests stretched until the last few decades, when necessity really forced Beijing's hand in looking further afield.
Even if China was interested in Korea, there is simply a chronic lack of good options for Beijing to peruse in Korea without risking making things a whole lot worse.
For the most part, China has pursued an exceptionally laissez-faire attitude towards NK, and was generally happy to let them go on with doing what they wanted, so long as NK didn't rock the boat too much as to damage Chinese core interests and threaten Chinese national security. That was the unspoken compact that was reached, and which daddy Kim stood by, and that was good enough for China. Even daddy Kim's nuclear ambitions was largely tolerated.
However, chubby Kim seems to want to play by a very different set of rules, and he is seriously peeving off China in doing so.
Although the west loves to portray him as a baffoon, it would be exceptionally unwise to underestimate him. The little pycho isn't an imbecile.
All those high profile purges he has been obsessed with are likely motivated primarily by his fear of an orderly, internal regime change orchestrated by China.
A lot of the senior generals and politicans he has been lining up in front of anti-aircraft cannons were likely key assets of China's - the precise kind of influential people China would have turned to, to remove chubb's round head from his padded shoulders and take over the reins of power in his stead should the need ever arise.
The exceptionally high turnover rate of top NK officials, especially military ones, would make it far hard, if not impossible, for China to cultivate the kinds of high level assets it would need if it wants a relatively bloodless and orderly regime change in NK.
Chubby Kim has spent his first years in power systematically hacking away at the safeguards and backups China has been busy putting in place to ensure that if NK ever goes try to jump off the deep end, China can yank it back off the ledge.
Just how much pull China has on NK has always been a subject of intense debate, but I don't think anyone would disagree that Chubb's purges have significantly weakened China's influence on NK.
However, I think Kim is playing a far more dangerous game than he might realise, and that his purges are a double edged sword.
While Chubb's making it more difficult and risky for China to engineer a regime change with minimal casualties and disruptions would reduce the likelihood of such a 'lateral' move, whereby the top man is changed, but much else remains largely the same as before, it does actually make a sweeping change more likely. Especially in light of the trouble he has been causing with his nuclear and missile tests.
If Chubb's crosses certain red lines (like directly and excliplity threatening a nuclear strike on China) and/or if his antics threatens to cause more damage to Chinese interests than a war, China may well decide that it is more in its national interest to ditch Chubb's and strike a grand bargain with SK, whereby China commits to helping reunit all of Korea under the rule of the South, and throw in massive reconstruction assistance, in exchange for the South kicking out all US military forces and allianing itself with China.
Chubb's purges of top military officials, like all such purges in the past, would have massively damaged the war fighting abilities of his already decrepit military, making a sweeping and fast victory much more likely.
Obviously, China and SK would much rather use an internal regime change to affect such a take-over, but the nature of such a bargain would make it exceptionally unlikely for North Koreans to accept it, so I think the only way such an unification could feasibly take place is through external invasion.
We are still probably at least half a decade off from such a scenario even being considered, barring some massive provocation from Chubb's in the meantime, and there are many essential pre-requisites that need to be met before either China or SK would seriously consider such a drastic move.
Firstly and most importantly, NK would need to become a great deal more unstable and threatening than it already is.
China would need NK to openly either turn its back on China, or betray China in some significant way, (like a threat of nuclear attack), as China would absolutely not want to be known as someone who stabs their allies in the back.
SK would need to invest in a massive active defense network for their boarder population centres, especially the Capital, to minimise the damage NK could do in the opening stages of any war.
It is still a far fetched fringe suggestion right now, but NK is pushing all sides towards it with each and every crazy move they make.