Korea is not reuniting any time soon. I imagine the only way that the South will reunite with the North is when circumstances force their hand either through a revolution or some sort of collapse in the North.
The North would be a gigantic welfare case for at least a generation, not to mention the stark ideological and cultural differences that have arisen over the last 60 years. I mean in a true reunification each side would have a say over internal and foreign policy. Can you imagine the South allowing that to happen, considering the huge GDP disparity? Can you imagine the North just signing on to be a vassal territory of the South without some extremely strong motivator?
Right now, the North is essentially a welfare case. Pretty much their entire GDP comes from imports from China, South Korea, and I kid you not, the US. Reunification would essentially shift China's role in North Korea completely over to South Korea. Since china currently donates the lions share of North Korea's "economy", this would a be HUGE burden for South Korea.
Not only that, but I can only imagine was sort of mess all the public facilities are in North Korea. It would probably take decades and billions of dollars to bring North Korea up to first world standards (And that would probably be mainly in the large cities). All the while, North Korea will provide pretty much nothing to the union. Their labor force would be mostly uneducated and provide very little to Korea's GDP.
Not to mention the tangled mess of getting everyone documented so they can work in better with south korea's current system.
For south korea, this would be a nightmare with very few benefits. The biggest being that they don't have to worry about their insane neighbor potentially shooting artillery into their cities.
China would LOVE it. They prop up NK right now just because they don't want to deal with some psycho with weapons shooting into Chinese territory. They also don't have to waist any money on NK any more, it would be a nice economic surplus for them.
The US would love it because they could move their military out and start to close down bases in SK. Plus there would be one fewer crazy dictator in the world to worry about.
The North Koreans might eventually love it. I could see there being a huge resistance from the people in the beginning, but I think after 10 or 20 years, they would be singing praises about how this is the greatest thing that ever happened to them (assuming SK puts in the time and money to start moving them up to first world status).
No, the only people that would really hate this are the current NK administration and the South Koreans. The two people that are needed for this to even be considered.
Why we gave back so much land to the North Koreans is beyond me. Most of the issues we have with North Korea could have been shrunk if we didn't give them so much freaking land. I realize that it would have been dicey to wipe them out all together, a war with china was the last thing anyone wanted.