Inside out World - our world is in the Light by Jim (aka Jjmckp)

After "What they died for" it seemed to become clear that the World is actually within the light, not outside the light. This interesting twist turns our whole perception of the Island inside out. I have not seen anyone state this yet - so I'll stop lurking. But there is more... read on

1) Jacob said clearly that what MIB wants is to get into the light - not across the sea. The plane is a red herring.
2) MIB has said several times that he wants to get off into the world. (We just assumed it was across the sea).
3) Several little inferences were made during Across the Sea that also seem to support this (looking in hindsight).
4) We have been told that life ends if the light goes out. It only makes sense if the world is in the light.

So what might it mean for our Losties?

We now know that Desmond, Hurley and others have an ability to reach through the 2 realities. But we also know that the front door approach (into the light) does not work. The backdoor approach is needed. (That said, Desmond may have a special front door ability.)
I am expecting that the Losties that survive the finale will actually be able to cross back and forth as needed (visiting Jack). Those that don't survive are mostly stuck in the Alt timeline world. Listen to the discussion with Hurley and Desmond in WTDF. Anna Lucia is not ready yet. Key word - YET.

Finally - There were clearly several Balls of energy or light buried on the island (Look back at the Map that Zoe asks Jin about). I might assume that these are slightly worlds. So, the initial world where the Losties came from might exist in one of them (the big one?), but the Alt world might exist in another.
What this means? - don't expect an answer to it in the finale. Where is the island in space time? What is the real world? are there more Islands in space time etc. These questions will remain and not get answered (but be fun to think about).
But, expect to see a big Lostie gathering at the benefit in the finale. Anyone guessing that Jacob may be the key-note speaker or the person being honored? ... or maybe even MIB with him?

We know it ends positively, if somewhat ambiguously. Theory above fits into that, but still leave much open for added reveals.