Already on their way there.To be like NK, China would have to shut off all tourism that is not state sanctioned. Basically you can only go where the country let's you.
Social credit score has that function already, too low score = no passport for you.Only allow travel outside of the country to the elite of elite or only CCP members.
See what happened with the Rome deal, China, unlike NK, has an extra option - money and corruption.Destroy any non state sanctioned religions.
But naturally, being defectors, they have seen plenty enough regardless, so that element kinda isn't working. NK is making defections a small scale problems through the harder means, like DMZ, family sanctions, and China being absolute dicks to defectors on their side of the border. Even in worst case scenario, defectors are less of a threat than rebels.What makes NK diffrent is they are supplied by outside forces. For instance watching NK defectors you can learn what all they do to keep the people oppressed.
Most of tjem have never seen a lot of what China has, let alone what South Korea or Japan has.
Considering the alternative, they would do their best, which we have only a limited idea on how well will that work, as no one in history has tested such a technologically advanced totalitarian state's resilience to rebellion.To make such a large country to be as isolated as NK, they would have to crack down and everything about thier country.
They would rather not need to, they have other, more optimized ways, but if that's all they have, i think they will try.China is way too big and populous, and its population way too educated (even if indoctrinated) to copy the NK model. It's not going to happen.