What's up with Kim Jong-un killing off his family's old guard without destabilizing the regime? North Korea might have a new military regime, with the new Kim as its puppet and/or figurehead. Anyway, that's the compelling case Christopher Lee makes:
Hearsay is circulating that Kim’s new generals—those officials he installed after he killed his uncle and others he charged with disloyalty or treason—are the brains of the operations. Considering this, a possibility exists that Kim Jong Un is a puppet ruler, controlled by the elites in North Korea’s government, similarly to the case of the Japanese emperor in the 1800s.
Under this Japanese model, the shogun (or in the North Korean case, military generals) hold the real power and the emperor (or Kim Jong Un) serves only as the face of the regime. If that were true in North Korea today, the generals would still need Kim Jong Un because the majority of the public still reveres his grandfather, Kim Il Sung—the founder of Juche ideology and the DPRK. It could also mean that Kim Jong Un may not have wanted to purge all the regents his father left him. Kim Jong Un’s closest allies were likely the high-ranking generals and politicians who sincerely supported Kim Jong Il throughout his tenure as the Supreme Leader. These regents were also likely the same advocates who stood by a dying Kim Jong Il’s side, promising that they would support the “Young Leader” and maintain the existence of the Kim family regime. Yet, a majority of these have since been either executed or relieved of their duties.
Kim Jong Un is now surrounded by new faces, only few of whom have ties to his grandfather or his father. Kim may have originally wished to rely heavily on Jang Song Thaek for advice on his reign, along with those other regents designated by his father, but something led him to eliminate these closest confidants. One may conclude that Kim Jong Un might have lost political power, but, as a descendent of Kim Il Sung and anointed successor of Kim Jong Il, he is still of tremendous value to the generals.
It's all conjecture, of course, since it's virtually impossible to know what really goes on inside the "Democratic" "People's" "Republic" of Korea. But an untested punk kid serving as the face of a military junta makes a lot more sense than an unrest punk kid personally killing off the old guard without imploding the regime.