“You, China, take NK out, and we, the USA will assure that Japan does not nuke up. And if you don’t, then, well.....Japan IS an independent country, and all, ya know....”
China may be willing to discuss that kind of deal, but they will never take steps to implement it. Words mean nothing. Commitment followed by action is all that matters.
China knows how to stall and drag things out to their advantage. So far, it is working for them, but not for us.