The problem with the article is that it assumes all the risks can be quantified and all necessary parameters can be defined, and all possible outcomes covered. It would be a reckless human that signed off such a study.
Do you seriously think that that the use of nuclear weapons to preserve American hegemony will have zero consequences from other players.
North Korea is just one more in a long line of countries destroyed by American Adventurism.
The pot is already boiling in the middle east, Russia, China, Iran, India, Pakistan all have their own agendas and have scores to settle going back decades. America has been at war 222 years out of 239 and is seen worldwide as a bully with no respect for international law.
Nuking North Korea could be just one more stupid move in an entire litany of stupid moves. Unintended consequences springs to mind.
In the past two oceans have protected America. I wonder what modifications you need make to a shipping container to launch missiles from them?
Other countries may also consider surgical strikes on America. Two can play dirty.