While I don't believe there is a conspiracy about Kim Jung Il's death - speculation on his health have been circulating for several years now.
However, if I were to make a conspiracy theory, I think James has hit the nail on the head
News reports indicate that he was on the verge of signing an agreement resolving tensions and accessing increased deliveries of food aid. As North Korea serves a very important functional role in the international system - that of the dangerous unpredictable nuclear power, capable of delivering nuclear missiles to half the world - any signs of a rapprochement to the rest of the world has to be fought.
Even in Australia we use the "threat" of nuclear attack from North Korea to integrate ourselves into America's satellite defence system. The military-industrial complex can not survive without exciting wicked villains and their viability and villain-ness has to be protected at all costs. And any North Korea that shows even the slightest signs of abandoning role assigned to that country must be ruthlessly eliminated - if nothing more than to encourage the others.