So, this is just a theory of mine on how a Alternate Reality would work in the LOST world. Don't worry, it's still WHH.
Anyway, back in S2 Desmond turned the key, which released all that electromagnetic energy, which made him MIND time travel. In his HEAD, he was in an Alternate Timeline.. he was never actually re-living past moments of his life physically, but mentally.
I think this is the exact same thing that will happen to... lets just say Jack. For a few episodes we'll be seeing a alternate timeline through the MIND of Jack. When the bomb exploded, it released all that electromagnetic energy, that I think will do this to him... True a bomb would kill them, but I think Jacobs TOUCH is what will send them back to 2007. So for a few episodes, I think we will be seeing 815 land safely, but only through the mind of Jack.
Then suddenly, we'll see Jacks "eye" opening on the island in 2007... and he'll be naked like Desmond was. He'll then find Kate, Hurley and all of the other 815ers that were touched by Jacob. He won't see the future like Desmond did, because Desmond just got lucky.. it was unpredictable.
So, there you have it... we'll get 3 timeline to START out the season: -A LITTLE bit more of 1977 stuff -A Alternate 2004 timeline through the MIND of Jack -2007 timeline(M#2, Sun etc.)
I think for these first few episodes we'll see 2007 stuff along with the MIND alternate timeline, so we'll get both... confusing the audience like, "didn't they change the future?" then we'll figure out that what happend to Jack is the exact same thing that happened to Desmond.. but Jack won't "future seeing" like Desmond did when he wakes up.
THERE! A way to please both WHH people and Alternate Reality people