Alternate possibility: Old Kim was in poor health, weak; power struggle occurred and new leader is decided; Kim Jong Il's death of natural causes -- with a little nudge -- is the last step. This is a not-unknown succession strategy in these kinds of regimes...

Further wild but plausible speculation: New leader may or may not be the son; he may be a figurehead for public consumption after he cut a deal to not immediately occupy the grave next to his father.
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