I think Kim is paranoid and scared. Maybe someone convinced him that he's the next Saddam, so he's getting ahead of it to avoid the same fate?
If Kim Jong-Un can pull things off right, he and his familiy will be able to live out their lives without having to fear being deposed and murdered, probably keeping enough wealth to live in luxury for generations, and maybe going down in history as a well-regarded peacemaking hero on top of it all.