Russia is loaded with natural resources and I expect control of most of them to fall into Chinese hands over the next 20-50 years. Putin may have wanted to reassemble the USSR but in reality he's weakening Russia so much China will eventually control all of it.
North Korea, on the other hand, doesn't have much to offer China.
On the other hand, most of what I know about these regions I know from podcasts so I could be entirely wrong about all of it.