What is North Korea's end game with some of these new weapons? Given that they have nuclear weapons along with a number of growing delivery platforms that having increasing survivability what exactly are they hoping to achieve through further military modernization?
If you don't keep your engineers preoccupied with new and challenge projects, their skills will fall into disuse, deteoriate, and you will lose an entire generation of skilled talent that takes decades to cultivate. NK didn't develop nukes overnight, took decades of technical training and development, you don't want to lose that talent by resting on your laurels.
Another reason is the national objective of reunification has yet to be achieved. Survival was the goal of KIS/KJI generation, KJU generation (with China as an ally) and onward will seek to evict all US troops from Korean peninsula, and eventually East Asia. If nukes alone were sufficient, why China bother with Liaoning/Shandong/Fujian carriers vis-a-vis Taiwan if reunification can be achieved by nukes alone. Nukes alone is not enough, it's a last resort option.
