I personally think they're setting up a situation where Christian figures prominently in Season 5.

But I can definitely see your theory. The island is some sort of spirit container, halfway in and halfway out of our world. This is why Miles was brought along on the "rescue mission," I assume. If we can believe Ben that Jacob is the ruler of the Others, then he knows how to control the container. How to turn it off and on, how to use it to his advantage...

One hole I see. Of course, doesn't John see Christian and Claire in the cabin? If I'm remembering correctly, then John didn't see a dead loved one -- he saw a dead stranger.

Ditto Michael on the freighter. He sees Christian just before he dies. No relation there, just a ghost summoning him to the island.

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