After watching 'LA X' and feeling somewhat satisfied with guessing the direction that the show has apparently chosen to head in for Season 6, I want to try and take a stab at posting another theory (which might refute my earlier one), in light of an EW interview with Darlton. After reading the interview, I'm wondering about whether the island sinking occurs not as a result of the hydrogen bomb, but as a result of Ben turning the wheel.
I'm abandoning my previous theory's use of "alternate" in regards to the second timeline that is created. Damon doesn't like it referred to that way, as it implies that it is not real. My sympathies to those who didn't like this reset stuff, but it seems pretty clear to me that what we're seeing with the plane landing is something Darlton feel is as real as the plane crashing. I also hope that those worried the show was going to completely eliminate the first 5 seasons have enjoyed that they will still get to see that play out.
One of the most important statements in the interview: "Should you infer that the detonation of Jughead is what sunk the island? Who knows? But there’s the Foot. What do you get when you see that shot? It looks like New Otherton got built. These little clues [might help you] extrapolate when the Island may have sunk." - Damon
I think this indicates that the island sinking doesn't happen in 1977, but rather, a time when Ben and the Others moved into the Dharma barracks. You could guess it happened any time after 1977 but my guess is that we've seen when it happened, in fact, we've seen it happen. The season 4 finale showing the island "moving" actually hid the answer the whole time. It didn't move through time. It did move, though - underwater. I remember at the beginning of Season 5, there was a fair bit of confusion about whether it was the island or the people skipping through time. I eventually came to the conclusion that it was the people going to different points in the island's history, meaning the island didn't move through time at all. In fact, it sunk when they all moved through time. This means anything we've seen set on the island beyond 2004 (including Sun and Frank meeting Ben and MIB/Locke; and now the events of 601: LA X after they travel through time to 2007) actually takes place on the new timeline. That's the main point of my theory: the 2007 island story from the second half of season 5, plus what we're seeing on the island now in Season 6 is happening in the second timeline that Jughead created. And the stuff we're seeing in the "flash sideways" is just a continuation of what happened after the island sunk in the original timeline. It's the opposite way round! The writers are going to pull the rug from beneath us and tell us that what we thought was the "alternate" timeline and what we thought was the original one is actually the other way round.
When the time jumping begun on December 30, 2004, the present-day island sunk to the bottom of the ocean as a result of Ben turning the wheel (but I hear you asking why the time travelers were still on the island - because when they went to the past, the island was still above the water for them to travel to. And when they jumped to the future, it was to the island that exists in the second timeline that was created as a result of the Jughead plan [which I'll get to later]. Similarly with Sun and Lapidus, they return to the island in 2007 in a different world). Of course, the most obvious question here then becomes why Richard and the Others were still alive despite the island sinking (ie. they were there the day Locke vanished in front of their eyes and they were there the day MIB/Locke came strolling to their camp, boar on his back, 3 years later)? Again, the answer is a different timeline. The timeline where Ben turned the wheel and Richard watched Locke vanish was the original timeline. In that one, Richard and the Others die when the island sinks, Locke travels back in time, as do 4 of the Oceanic 6, allowing them to go on separate journeys that eventually lead them to creating (via the Jughead method) the very alternate world that Richard and the Others greet MIB/Locke in when he strolls in with the boar, the same world we're now seeing in the Season 6 island story, the same world that Ajira 316 crash landed in, the same world we got a glimpse of when the time travelers saw the Ajira bottle in the outrigger. Essentially, that world was shown to us before we saw how it got created. Even for the characters, they arrived on it in 'Namaste' before they created it, so that they could create it, leaving another perfect ridiculous paradox for us to bend our minds over.
To try and wrap this up, I'll give an outline of how each timeline played out, based on what we as an audience have seen.
The first one: Oceanic 815 crashes, they live for 3 months, Ben turns the wheel and the island sinks as half the survivors go back in time and the other half leave the island. They all then meet in 1977 where Jughead creates the second timeline.
The second timeline (I'm not saying it starts in 2007 but our first experience of it is): 2007, Ajira crash lands on the Hydra, they all eventually cross to the main island and meet at the statue foot. Jack, Kate, Sawyer, Hurley, Jin, Miles appear out of thin air on the night that Jacob is killed and they begin their journey to the Temple.
And what we're left with is, the Temple+MIB stuff happening in the newly created timeline, and the "flash sideways" stuff happening in the original timeline, which we haven't seen any footage of since Ben turned the wheel in it.
But then where does that leave what we've seen in LA X's "flash sideways?" Where does that stuff fit into the two timelines I've just laid out? If Ben sinks the island in 2004, and the plane flies over the sunken island, that obviously has to take place after 2004. I don't have an answer for this because I think that links into how the two timelines will converge, which will be the payoff toward the end of the series.
I'm rushing this onto the blogs so that it can be digested before the next episode, in case the next episode completely refutes it, so hopefully it's as succinctly and easily laid out as it could be.