As the article makes clear, China is a big part of the reason North Korea has managed to develop nuclear weapons and missile capability. North Korea is useful to the Chinese leadership as a way of tweaking the US's nose and intimidating other Asian countries, in particular, South Korea and Japan.  However, what would counter that and be a strategic fiasco for the Chinese leadership is the rearmament of Japan, including ABMs, and possibly including a complete MAD capability. (Ronald Reagan was supposedly told in the 1980s that Japan could develop nuclear capabilities in six months if it so wished. )  Instead, the Chinese leadership seems to have been oblivious to this potential consequence of North Korea's nuclear ambitions.