Where does NK get an enormous population like China's? Without kazillions of cheap workers, the NK state will never be as well off as the Chinese state, and without that they may not be able to control their population/fend off the outside world.
North Korea has a population the size of Taiwan. Small populations make it easier to raise the standard of living. Considering NK had higher GDP per cap than China in the 80s, they should have an easier time reforming the economy.
In such a scenario North Korea will avoid the famines it suffered OTL and certainly be heavily invested by South Korean investors. Look at the success of the Gaesong Industrial Zone in OTL now imagine x10000.