Don't we have these exact types of sanctions already in place i. NK for exactly the reasons you mention?
The people are severely repressed, it's hard to imagine how much North Koreans suffer, look up Yeonmi Park's story.
What we seem to do is ignore these maniacs, until it's too late or it's absolutely critical, then they hold us hostage, like Putin.
(edit: another old article that points out inconsistencies in Yeonmi Park statements: https://thediplomat.com/2014/12/the-strange-tale-of-yeonmi-p... ... The JRE interview wasn't a fluke)
I don't think that you can reasonably treat Yeonmi Park as a reliable witness.
North Korea's train network is 4700km long, though it is not perfect... If you want to travel from Pyongyang to Chongjin for example, you're better off flying there