possible spoiler below... highlight if you want to read it.
Not really a "theory", but major plot leaks from a reliable source, whether you believe them or not. The reliable source is someone who works somehow related to the production of the show, and when the producers agreed to the deal for the show to end in 2010, they had to draw up a general plan for the show until then. Logically you would assume only a few people would have access to this, but in fact these facts came across a lot of people. So somewhere in that line of people came the reliable source, and here is me relaying it. I promise I'm not the source and i promise I'm not changing anything i've heard.
If this info has gotten to me, and consequently to you, whoever's reading, then obviously the producers will find out and may change things. I don't know. But this is just what I've found out and this is coming straight out of the plot outline the producers needed to draw up.
- There will be 3 "flash-forward" episodes 2008 season, 3 "flashforward episodes 2009 season (including its finale), and 10 of the 16 episodes in the 2010 season will be flashforwards.
- The 2008 season will begin with a "New character"-centric episode. All we konw is "new character"
- 2008 season premiere has partially been filmed already. The rescue does not occur by helicopter. They meet the ship on shore and the "rescuers" come on smaller boats.
- In the 2008 season premiere, during the episode a timespan of 2 days elapses, in which the "rescuers" get the Losties ready to leave.
- In the 2008 season premiere, the "rescuers" take body count of all who are buried on the beach or have died on the island, and Hurley will give brief synopsis of dead characters in monologue with flashbacks
- The Temple is a building, but mostly underground and is the first major set to be built for next season. Will include many "technological" props, such as monitors and computer switchboards.
- Sayyid is killed at the end of the Season Premiere as he discovers that the "rescuers" are Dharma Initiative. Naveen Andrews will continue to reprise his role throughout the remainder of the series, possibly in flashbacks. (Or maybe he doesn't really die, who knows)
- The character of Hurley will die during course of 2009 season. Unknown why or how, and whether his actor will come back for flashbacks.
(Here's where the info is kinda all over the place)
- Polar bears appear in the 2nd episode of the 2008 season
- Desmond gets out of the hatch in the 2008 season premiere
- Locke does not return to the show until severeal episodes into the 2008 season
- Explanation that is revealed near the end of the 2008 season: Dharma Initiative has created a "time door". One end of the door exists in present time in Antarctica. The other end of the door is the Island. However, the Island exists in the "time bubble" in which it remains in the past. Everytime someone (Desmond) pressed the switch in the Hatch, the Island was reset further back in its own time, while the present continued onward.
By nearly not pressing it, it opened the time bubble slightly, and Oceanic went through the bubble and crashed into the Island. When the hatch exploded, the time bubble was released, and accelerated into the present. It is Jack, Jin, and Desmond who come upon this knowledge by the leader of the Dharma Initiative in the Season Finale of 2008.
- 2009 season opens with a Ben-centric episode.
- 2009 season focuses on time travel, and several times characters will return to the "past" and revisit scenes from previous episodes.
- Michael will return to the cast in 2009. Unknown if Walt will.
- Smoke monster is defeated in 2009 season.
- Matrix-like storyline is presented in 2009 season, where "present" may actually be another time bubble. Dharma Initiative seeks to find an even farther "future".
- Jack discovers sibling relationship to Claire in 2009 season.
- 1/2 of the Survivors are "rescued" in 15th episode 2009, but time machine explodes. They are sent into a parallel time bubble which is a prison in a snow-bound place. Sun, Sawyer, Claire, Ben, and apparent new characters Rex and Toasty (code names for characters they haven't thought of yet?) are among the stranded.
- Juliet ambiguously dies in 2009 Season Finale.
- Dharma Initiative Conspiracy is revealed in 2009 Season Finale. Christian Shephard, Mr. Paik, Charles Widmore, and Richard Malkin are named as some of the members of the Dharma Initiative. Oceanic was intended to fly into different "time bubble", but when Desmond failed to press the button in the "island time bubble", Oceanic was caught between two time bubbles and crashed into the "island time bubble", which was deserted by the Dharma Iniative after Ben took it over.
The Operation was intended to place loved ones/friends of benefactors of the Dharma Initiative in a time bubble where they would be safe from an oncoming world catastrophe. The passengers of Oceanic were considered thsoe family/friends that would not willingly go through with a passage through the "time door" in Dharma Inititive headaquarters in Antarctica, therefore were brought together on Oceanic in order to safely land them on a new "Paradise" Island. However, the Operation failed when Desmond's mistake caused all incoming 'deliveries" to the "Paradise" Island to catastrophically land on the Island the survivors are now on. The 2009 Season Finale ends with Dharma showing the survivors the "Paradise Island", but once there, they realize it is desolate, and hundreds are inexplicably dead on this island. Jack finds his own dead body on this island.
- The 2010 Season Finale begins with the rescue of the survivors stranded in the Dharma "Prison bubble". All survivors/Dharma are returned to the original island by the 3rd episode.
- There is no more time travel (between time bubbles) in 2010 season after the Season Premiere. Focus is on getting rebuilding the "door" in order to be transported back to the present
- New faction of survivors/Dharma are led by Locke and another character simply named Black-suit (again, maybe a code name for an as of now unknown character), in an attempt to not allow anyone to leave the island in 2010 season.
- Yunjun Kim will relatively be absent for most of the 2010 season. No details on whether she is killed or not. Jin, however, is mentioned throughout the details of the 2010 season.
- A new smoke monster is built in the 2010 season.
- Juliet returns in 5th episode in 2010 season., only to die at hands of Sawyer in order to save everyone from new smoke monster
- Mikhail (yes, some-freaking-how) is mentioned as setting off a bomb that causes the "good" group of people to be split up on the Island in 2010 season.
- Ben is killed by Locke in 9th episode of 2010 season, titled "Hunger of Memory".
- The series finale comprises a final confrontation between Jack and Locke in a new "hatch".
- Here is the list of people "transported" to present time at the end of the 2010 season finale: Ballerina (?), Tap-Dancer (?), Kate (we know her), Sawyer (anotehr one we know), Musky (?), Jin (know him), Jack (yay), Claire (what about her baby?), and someone simply named Insert (yeah, Insert).
- Many, many names for deaths in series finale, here are some interesting ones: Catholic, Tape, Cus-cus, and Doc. Lets look back on this years from now and figure out who they were referring to.
- Among the names that we do know for death in series finale, are Desmond and Penelope (I don't know how the heck she gets on the island).
- Series finale ends with survivors in Dharma headquarters. They are asked to keep a vow of silence, and in turn are promised a return to the "Paradise Island" once it is ready. The survivors are again transported back in time, to when Oceanic crashed. The crash now actually occurs in present time waters, and unbeknownst to the passengers, Jack and the others are from the future (past, whatever the hell they're from). Oceanic crashes, but all the passengers survive.
When returned home, all the passengers become media icons. However, Jin is now with a Sun who does not know about what happened on the island, and must reconcile with her, without those experiences he had on the island. Kate is immediately brought into custody, but her charges are lessened due to the circumstances, and she has saved Boone's life in this plane crash. Claire gives birth to her baby at the end (possibly her "island" baby has died?). Months go by and those who were part of the series' events are not contacted by Dharma. They meet together and want to just let it go. Some want to try to find the Dharma Initiative. However, Dharma warned them that if they tried to find them, they would be killed.
Sawyer is killed in a "random" shooting. Jack is convinced it is Dharma behind it. Kate disobeys are parole officer and goes with Jack to confront Sun's father. There they meet Christian Shephard, supposedly from some kind of future or something. Christian explains that the Dharma Initiative has failed and was completely destroyed. Christian refuses to kill Jack and Kate and lets them go. Kate cannot return to the public because she is a fugitive. Jack has killed Sun's father as well. They retreat to an island in the Pacific and Lost ends with them sitting on a beach there.
