The article doesn't describe the type of rare earth...

The article doesn't describe the type of rare earth deposits in North Korea. They, like China are probably light rare esrth containing carbonitites or clay deposits. These light rare earths are already abundant as reflected in falling prices and the West is unlikely to source rare earths from Nortn Korea for security reasons.
The attraction with Greenland is the higher concentration of more valuable, rarer, magntic heary rare earths elements
Bureaucratic impediments are more often a bigger problem than political impefiments in developing new depisits