At no point is Kim Jon Un a rational state actor.There's nothing inherently wrong or infeasible with appeasement as a foreign policy, so long as you are negotiating with a rational state actor. Hitler was not a rational state actor. These days, pretty much everyone, even Iran and North Korea are rational state actors once the nuclear factor enters the equation. When their very existence is at stake, there's a tremendous amount of incentive to approach diplomacy from the perspective of a rational state actor.
And I am wracking my brain trying to think of the last time appeasement had a good ending. I'm as far back as Ethelred the Unready, and it didn't work for him, either.