Buffer zone, against what? With Hong Kong absorbed, and their economy moving toward a freer market, letting their people see a free market working might be a good lesson for them. "Work hard, and this is within your reach!"
As for a military buffer, they have bigger problems in Russia, India, and the Islamic states of central Asia. And they fear a flood of refugees from NK, so giving them somewhere else to go where someone else will help them might be a positive idea.