The scary thing to me-- my first thought is if something like this happens and is successful, they would no doubt blame the US and say it was an assassin, and lead the march to war. These people are nuts!
Better that Kim Jong Il stay around for now, the enemy nutcase we know is better than one we don't... If nothing else, he's not irrational. He wouldn't thrust into S. Korea unless he thought he could win quickly. And by moving the bulk of the U.S. forces to the south (not to abandon the DMZ but to ensure our forces survive an NK first strike), he knows he would have a long bloody fight if he tried anything..
In any event, for such purposes, better he remain in power for now...