Here is the problem with that:
1. South Korea would need cubic bucks from the US to rebuild North Korea.
2. No demoncrat would permit it. They would kill all Republicans, starting with Trump, just to save some face.
3. China and Russia would not be thrilled with sharing a border with a capitalist power house. They would work HARD to overthrow the ROK government, and with as many communists as there are on South Korean campuses, they might just manage it.
Just saying some things to consider...
We rebuilt Europe via the Marshall Plan, specifically to stop Communism.
We can do it again.