A Long Game of Go by Jergar

I would put forward the idea that Jacob and MIB are playing a long game of the board game Go. The prize to the winner, at least to MIB, is that if he can turn all the chips (people on the island) to his color, he can have his way and go home. And the island is destroyed and sunk to the sea floor.

I think his means for turning people to his color is becoming obvious-- promising them a new life off the island with their dearest wish granted. Sayid has Nadia in his life (all he told Flocke was that he wanted to see Nadia again), Jack has his career back and peace with his memory of his father, and Hurley no longer feels cursed. Also, in the ALT timeline, Kate has escaped the law, and Claire has Aaron back. I think the season will develop as we see the ALT timeline as one where all the island inhabitants have been granted off-island lives that roughly (though not perfectly) fit their heart's desire. In return, they give their service to MIB to help him win the game.

How the series will end though, I do not know. I have not factored Desmond into this theory, I think he will be the most important figure in the ultimate outcome of the game.