The media continue with their “great man” model of leadership with regard to Kim Jong Un’s succession. They imply if things are happening, the person in the leadership position must be making them happen.
I think a systems perspective more accurately describes the situation.
For example, today’s New York Times describes him becoming

“supreme commander” of the military, signaling that his succession is moving forward unimpeded.

They imply some chance of someone impeding his succession. I expect anyone with influence would, if anything, help him, for stability and their own safety.
More odd implication, that he is consolidating control:

The military’s support is considered crucial to his consolidating control after the death of his father

If anything, I expect everyone is helping him. Everyone with influence knows the stability of the system that protects them. They just need someone’s face next to Kim Il Sung’s and Kim Jong Il’s. His youth helps them — it means longer stability as long as he lives.
Another odd implication:

The state-run media’s call for Kim Jong-un to lead the military suggests that, at least for now, he is on pace to take full control of the country.

I wouldn’t say he is taking control, but that he is assuming the role in the system that his father vacated that no one else would fit as well.
I don’t mean to say Kim Jong Un won’t have power, but I expect mainly for his personal whim or benefit — to do things that don’t affect the system. Kim Jong Il was famous for indulging in expensive food, punishing others, ignoring the plight of his people, and so forth.
I doubt he’d get far liberalizing the economy or opening the borders except under pressure from outside the system, like the population learning about the outside world and reducing their support.
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EDIT:  misperceptions of North Korea in the media as described in this post, leading to misunderstanding how we understand and commincate with North Koreans, led me to write my ebook Understanding North Korea: Demystifying the World’s Most Misunderstood Country. I wrote the book to help increase understanding, communication, and freedom.