http://www.businessinsider.com/north-koreas-and-marijuana-2013-1
I think a lot of things would have to go right fo this to happen ... and, I suspect none of them will. Even if they do, the weather and general geography don't support the idea.
For one, South Korea would basically be running the show after reunification due to the larger population and the fact that there is no culture of participatory democracy in the North. In the South, cannabis laws are VERY restricted, so much so that a South Korean using maijuana overseas can be prosecuted under the criminal code upon his/her return to S. Korea! If the political domination of the unified penninsula by the South comes to pass they will surely overturn this law.
Secondly, who wants to go to Korea? The weather is not so nice and, unlike Amsterdam, it is not some localized hub close to other places you might want to pop off to with a backpack on a train ... in fact, it is an isolated penninsula.
I think the only way for this to happen would require larger geopolitical tends to occur.
Aging china with a falling population is hit with a slowing economy and social unrest. They can no longer afford the same investments in North Korea to prop it up ... like Cuba after the fall of the USS, N Korea decides to liberalize its economy somewhat, and it bings in Russia technocrats to help since (a) China is a bit distracted, (b) they want to diversify their patrons, and (c) Russia learned a lot from the failed opening of their political and economic establishment.
One thing Russia advises and North Korea accepts is the promotion of eco touism since so much of the country is virgin natue due to underdevelopment. At this time - say the late 2020s - eco tourism is booming along with the general global economy and North Korea begins to benefit from the adventerous fist touristy pioneers to come. These first travelers are invaiably young, and they discover the amazingly liberal cannabis laws while in NOrth Korea, word begins to spread, and photos pop up on social media of friends smoking grass on a mountain or somesuch.
Tourism increases and North Korea discovers that creating government sanctioned coffee shops w/ cyber cafes is a great way to slowly integrate into the global economy while still maintaining control and vigilence over online activities of their citizens and visitors alike.
Now ... when/if unification occurs, the economic entrenchment of pot tourism will be much stionger than just lax cultural and legal attitudes, N. Korea will be moe developed, and South Korea cannot strong arm it into changing its laws.
The implication would probably be that some, especially Australians and New Zeelanders who do not want to travel so far for a quick drug holiday, might make the flight to Pyongyang ...