Kim Jong-il takes more power in the 1980s from his father when he was much more reformist (Lets say Kim il-Sung has a stroke in 1982 or something, leaving Kim Jong-il in power to run things. Kim il-Sung is still alive, but at this point just keeps the military at bay and makes public appearances). Kim Jong-il in the 1980s was much more of a reformist, so if he brings up North Korea's economy by the 1990s, and follows through with his father's plan for a "Two-systems, one country" style unification by the 1990s or early 2000s, I could see him getting a Nobel Peace Prize.
Or even if he just ends the isolation by the 1990s and makes reforms like Deng Xiaoping.