The ALT universe is the losties reward for their 'deal with the devil' by Sepia Jack

After watching 'Sundown' again I'm convinced that the flashsideways/LA X timeline is not a product of the jughead bomb being detonated in 1977, but instead is a result of MiB escaping the island.

At first I thought the season would be ghost Jacob & MiB each recruiting the various Losties onto their opposing sides of the battle, but now I'm convinced that by the end of the season EVERYONE will have joined MiB. Jack, Kate, Hurley, Sun, Jin. Everyone.

I think they will be tired of Jacob's cryptic indirect answers and the island mysteries (a metaphor for many fans?) and they will all fall under the influence of Locke/MiB. Either in the finale, or just before the finale, they will all leave the island with him (I'm still assuming that the Others have some sort of stargate or portal to go back and forth from the island, how else did Tom go to get Michael when the submarine was not an option? and how did Alpert go to see Locke as a child?) and the result of him leaving will be what causes the island to be underwater.

He told Sayid that he could have 'whatever you want' (is this all going back to the magic box?) and I think the LA X universe is the result of that.

This would also mean that MiB would be in the LA X universe, and perhaps the finale would be the Losties coming together, realizing the error of their ways and battling him in the real world.