NK is a complete basket case, with a population that has been brainwashed by 70+ years of misrule, a development level probably below China in 1949, and they have a different language and culture.
Right now, China gets the benefit of a buffer state without the downside of fixing generations of problems. They would take the blame for every problem.
Did you know that the goal of reunification is explicitly written into South Korea's constitution? Yet I've spoken to younger South Koreans -- even they don't really want to reunify with the North, because it would significantly lower the reunified country's standard of living.
It took an entire generation for East Germany to reintegrate with the West, and even now GDP per capita is about 30% lower in the east. And East Germany was only about 20 years economically behind the West. For NK, multiply that problem 10x.
I mean what do you want to do with NK? Leave it be? Laissez faire? Let it develop nukes as a "deterrent"? Let it be aggressive? This will not end will for the region if something isn't done, and SK is reminded that on a daily basis.
The problem is that nobody knows, and nobody wants to be responsible for figuring it out, implementing it, and paying all the costs. We're all hoping somebody else will fix the problem for us.
The US blames China. China predictably blames the US. South Korea vacillates between being hot and cold towards its Northern brother, yet neither approach has solved the issue. Meanwhile, Russia is all too happy to no longer be associated with the problem in the eyes of the global public, despite its own key role in getting us into the current mess.
You're right that reunification still has majority support in SK, but will that be true in 20 years' time once a unified Korea can no longer remembered by anyone still living?
If China was considering this type of thing, it would be a split of NK territory between itself and South Korea. China would be holding secret talks with South Korea about militarily assisting them to reunite with the North, in return for China getting some of North Korea's territory. After the initial show of strength, China would offer top NK leaders and military officers lifelong residence in that annexed territory, with immunity from deportation. The U.S. right now is probably trying to stop such secret talks from starting, probably by impressing on the SK govt just how much their standard of living would be impacted by reuniting with the North. Of course, China would be using this as leverage in the secret negotiations to gain as much NK territory as possible.
The Kim dynasty has shown zero inclination to give up power, which would make such a concept a nonstarter. If DPRK could be solved by all parties other than the Kim regime (say, by decapitation of the regime and containment of the resultant chaos), it would be a done deal. Everyone's been hoping the regime would collapse before becoming a credible nuclear threat, but that hasn't happened and the temperature keeps rising.
I think we ultimately will live to see this play out. I have to assume it's being negotiated even now, because it will be require unprecedented coordination to defuse NK without massive civilian deaths in Seoul or a refugee crisis in Manchuria.
As far as I know, China does not want NK territory. The last thing they need is an extremely insular ethnic group to integrate. They want containment of NK and less US presence in Asia. They also want Taiwan, but I think a much diminished US presence on the peninsula would be more than enough for them.
This makes sense. NK is valuable to China as a buffer from Western countries. I'm surprised by this announcement simply because from that strategic perspective, it hurts China. If they plan on annexing, that makes more sense.
If they do, I'm sure we won't do much to stop them. We'll complain (us Westerners) but when the rubber meets the road, China is a better holder of that territory. Our only concern will be annexation of SK by China after NK, but I find that unlikely within the next 20 years.