A former ambassador and defector Thae Yong-ho says they are. He's indicated multiple times that the elite is beginning to chafe against the restrictions of Kim Jong-Un's regime. He's also indicated that dissent and criticism are becoming more and more public and outspoken. So it sounds that way. I'm not sure what purpose he'd have to falsify such things.
The rule of Kim Jong-un is coming to an end. A high placed defector who knows the situation well has stated this to be the case. Jong-un has alienated his one ally, China. Meanwhile, his country is an economic mess, and the trend towards more information cannot be stopped, even by a dictator.
In the last few years, many dictatorships have fallen. Qaddafi, Mubarak, Ben Ali and a few others have seen their iron rule break. However Kim Jong-un rule is different to his predecessors. He has sought to improve public relations. He has also increased foreign direct investment. He even has gone so far as to open up for tourists and allow foreign students.
Kim Jong-un may not be able to rule North Korea forever; however, his rule is not likely coming to an end anytime soon. Kim Jong-un still has a lot of power over the North Korean government and security forces. It will be very difficult--if not impossible to depose the leader.