I had a chat with a Korean expert at lunch today. Here's his read on the situation. China has been using North Korea as a buffer between itself and South Korea The U.S. forces in South Korea are that much farther away from the border with China. As such, China is decidedly not interested in any kind of Korean unification. Given the level of Chinese pull in North Korea, they could very well decide they've had enough with the present North Korean government. At that point, the only remaining question is exactly how hard they'd have to push to overthrow the government and install another one.