The Final Trip
This theory is a result of a discussion AES and I had in his post “Achalli Knows.” This is his theory just as much as it is mine. One of the books that the producers have admitted to as inspiring them is the Illuminatus trilogy by Robert Anton Wilson and Robert Shea. And a major plost point in the book may hint at what to expect in the FSW.
The Illuminatus trilogy is a rather lengthy work and takes awhile to get used to its style. What follows is an excerpt from Wikipedia that describes what is hapenning towards the end of the book:
The evil scheme uncovered late in the tale is an attempt to immanentize the eschaton (a catchphrase meaning “bringing about the end of the world” or “creating heaven on earth”, and derived from a quotation in the works of Eric Voegelin). Here it refers to the secret scheme of the American Medical Association, an evil rock-and-roll band, to bring about a mass human sacrifice, the purpose of which is the release of enough “life-energy” to give eternal life to a select group of initiates, including Adolf Hitler. The AMA are four siblings who comprise four of the five mysterious Illuminati Primi. The identity of the fifth remains unknown for much of the trilogy. The first European “Woodstock” festival, held at Ingolstadt, Bavaria, Germany, is the chosen location for the sacrifice of the unwary victims, via the reawakening of hibernating Nazi battalions from the bottom of nearby Lake Totenkopf. The plot is foiled when, with the help of a 50-foot-tall incarnation of the goddess Eris, the four members of the AMA are killed: Wilhelm is killed by the monstrous alien being Yog-Sothoth, Wolfgang is shot by John Dillinger, Winifred is drowned by porpoises, and Werner is trapped in a sinking car.
The major protagonists, now gathered together onboard the submarine, are menaced by the Leviathan, a giant, pyramid-shaped single-cell sea monster that has been growing in size for hundreds of millions of years. The over-the-top nature of this encounter leads some of the characters to question whether they are merely characters in a book. This metafictional note is swiftly rejected (or ignored) as they turn their attention to the monster again. The threat is neutralized by offering up their onboard computer as something for the creature to communicate with to ease its loneliness. Finally, Hagbard Celine reveals himself as the fifth Illuminatus Primus – he has been toying with both sides and playing them off against each other in order to keep balance. He is a representative of the “true” Illuminati, whose aim is to spread the idea that everybody is free to do whatever they want at all times.
The parts to pay attention to in the description from Wikipedia is the number of Illumini Primi and the attempt by the AMA to induce a mass human sacrafice to utilize their life energy. Now, take into account that, counting Desmond, there are five canidates left on the Island. Also, the number 5 is a part of Jack’s tattoos. And there are 5 Illumini Primi in Illuminatus.
So how to apply all of this to Lost? Basically what AES and myself are thinking that will happen in the FSW is this, Desmond and the Losties are all going to die at the same time, most likely by sacraficing themselves, and release the Light that is in them. The released Light will be channeled back to the Island to be utilized by the Losties there to defeat MIB.
Another thing to note that is similar in Illuminatus and Lost is the use of the Celine system. Hagbard Celine developed a system for getting people to join his cause and this system often involved getting the person to a point where the their mind basically shuts down and the body runs on auto pilot. More often than not Hagbard would take the person to a point of near death. Desmond seems to be doing the same thing with the Losties in the FSW and may be doing so for similar reasons.
I know AES has some more to add to this and will leave of here to continue discussion in the comments.