Three of China's top 5 trading partners are the US, Japan, and South Korea - it's economy has thrived for the last decade+ because of those nations most impacted by North Korean threats. China may not have that much leverage, but they know where their bread is buttered. More importantly, China wants to be a global power. The US government policies while directly failures vis-a-vis North Korea, also highlight China's impotence to other players on the world stage. To take that final global power stride, they will need to deal with North Korea at some point.
Bigger picture, I feel like whenever these kind of analytical pieces surfaced in the past, they rightly always included a point about proliferation, something that seems missing these days. If the world moves on and grudgingly accepts North Korean nukes, what stops Japan from getting one? How about Taiwan or South Korea? Same concern goes with Iran's program - what stops Saudi Arabia, Turkey or Egypt from getting one?
It is a slippery slope argument, but the consequences of the number of nuclear powers doubling are pretty dang grave, maybe it is one slope we can keep an eye on.