At this point the DPRK is becoming more of a liability to China than useful. China has stronger commercial ties to the US, South Korea and Japan than it does North Korea. Right now they would rather bully Southeast Asian neighbors with their new toys (a deepwater navy) than really confront developed nations in a significant fashion.
The real big worry people should have with the DPRK’s nuclear program is the high likelihood of a Chernobyl-type disaster. That the carelessness and backwards technology will unleash a radioactive mess which has Seoul, Beijing, Pacific Russia and Western Japan in its footprint.
