The article also mentions the savings to their economies by not having to support two huge standing armies. That there will put a lot more people in the work force.
Politically it will be difficult trying to mainstream a large brainwashed population such as NK has into the 21st century and that will cause a lot of strife and will probably be the most difficult part of reunification. Unlike the East Germans, who had a very good idea of what things were like on the other side, the NK populations is still largely brainwashed.
The article also mentions that Russia and China are already working on building the infrastructure up in NK as they are both anticipating a major change in NK. Between the SK, China and Russia I don't think it will take as long as you think to to get NK up to par. Russia has a huge source of natural resources that is readily available to NK and they have improved the train tracks going into NK and the Chinese and Russia are already modernizing ports.
Unlike West Germany, which had a huge expensive welfare state ready to absorb the East Germans, the South Koreans do not but they don’t need one as both populations are use to not having a nice cushy safety net to take care of their people. A lot of East Germans were content to live off this system but that will not be tolerated in a united Korea. That will be less of a drag right there.
The difference is North and South Korea have been separated for 70 years. The average IQ of the south is 10-15 points higher. The average height is 4 inches shorter in the North.
The Germanys were separated for roughly half that and East Germany was the largest economy in eastern Europe. That took 20 years to fully integrate.
The reunification of the Koreas will take considerably longer.