Clarification: By SK and Japan going nuke, I meant they would become nations with nukes. The perceived threat from them having nukes would be on the part of China, not NK.
"The perceived threat from them having nukes would be on the part of China, not NK."
? would either of them being perceived as having nukes be a threat to China ?
Both of them have major nuke power in operation, so hiding a bomb project would not be a big deal.
I suspect that either of them could pop a nuke blast within months.