Stick with me here (it's gets good!!!)
I am reminded of a line spoken by Alec Baldwin in the twisty thriller Malice from 1993;
"So I ask you; when someone goes into that chapel and they fall on their knees and they pray to God that their wife doesn't miscarry or that their daughter doesn't bleed to death, who do you think they're praying to? Now, go ahead and read your Bible, and you go to your church, and, with any luck, you might win the annual raffle, but if you're looking for God, he was in operating room number two on November 17, and he doesn't like to be second guessed. You ask me if I have a God complex. Let me tell you something: I am God."
And I think Jack, currently in 1977, is acting on the whims of this common complex of the ego that surgeons do suffer with and he believes he can change things for the better. Typical of a Doctor who always wants to fix things. But I think The Universe may have something to say to Dr. Shepherd before the lights go out on Season Six....
There has been so much talk of resets and alternate timelines etc. I personally prefer keeping things simple with one timeline but I got to thinking about the idea of an Alternate timeline and realised that if Jack has created a second alternate timeline branch where 815 never crashes, and where all the "misery" they endured never happened, then indirectly Jack causes the end of all mankind. His actions will provoke the ultimate course correction and by using cannon mythology from the show I'll highlight this in neonlight signposting.
So, we know from Hawking (Lost's Hawking, not the real guy) that "the universe has a way of course correcting." I think the universe does not like having more than one timeline at any one time. But let's say Season 6 will be a reset alternate reality that for us viewers will run concurrent to the Flocke future/present timeline (two timelines instead of a flashback/flashforward structure).
The alternate reality, this new timeline, will only last 40 or so days after 815 lands in LAX because without John Locke ON the island and without HIS discovery of the hatch and his subsequent Deus Ex Machina angry/distraught hatch door beating - Desmond never regains hope that the outside world is still there and therefore starts to read Charles Dickens Our Mutual Friend, the last book he said he'll ever read before he dies and then as the events of the Season 2 finale suggested that he was going to do had Locke not caught his attention that night - Desmond kills himself. This will leave the button unmanned and the timer will tick down causing the electromagnetism to build up in a globally catastrophic event essentially killing us all.
Now, here is where my theory comes into play for the show. I now believe the writers will show the the end of the world happen by way of this new alternate timeline. So, while we watch the new season, completely confused as to what the real timeline is between seeing the 1977 shenanigans, Flocke's leadership in 2008, and this potential alternate timeline of new events post 815-landing at LAX, all will then be made clear in the last episode (I'd say around epidodes 10-12) that shows the alternate timeline version of events - and it ends with a bright purple light in the sky, a montage of our alternate timeline Losties in their respective alternate lives witnessing it in awe/horror and the universe's course correction / destruction of this paradoxical new time branch that should not exist. Yes, Jack's plan will work, but fate/the universe will correct that mistake as you can't beat fate's plans. Lost will show us that whatever happened CAN BE changed but then CORRECTED (eviden! ce of this: Des and Charlie in Season 3.)
If you want to take this theory further here's how it could potentially answer something. For those of you who have asserted and supposed Jacob and/or his MIB friend were time travellers from the future, perhaps they were not from the original Losties timeline (i.e. 815 crashes timeline) perhaps they were from this alternate timeline where the world does end. Jacob (whoever he may really be) is somehow intentionally or unintetionally thrown back in time and begins to manipulate events to change this outcome of Desmond failing to push the button on September 22nd which leads to his suicide a month later. I'm not fully behind this aspect of the theory regarding Jacob time bouncing a la Sam Beckett as I am not fully convinced that either Jacob or his enigmatic friend in black are anything like gods/time travellers/magicians/comedians/whatever etc.
Part of me believes that Jacob is merely a man who has extraordinary knowledge, while MIB...
Okay, my theory on him - if he is the smoke monster (which again, many have asserted) then the actual phsyical form we see it in at the beginning of The Incident is nothing more than a man who died on-island and the smoke monster has merely taken his form in order to manipulate and taunt Jacob. The MIB is not the Smoke Monster, but the Smoke Monster is the MIB if you get me. The smoke has always been smoke. The only time it is in human form is when it takes the shape of a human. MIB is merely another one of its dead vessels/duplicates. He was probably someone Jacob knew from before as I am sure we will discover next season. MIB is a vessel, not the monster in original form. It's original form IS the smoke.
Anyway, in a nutshell - Jack does not change the future, but merely creates a new timeline that runs concurrent to the original one, only the universe will course correct it when Desmond does not get "saved" by the pained cries of John Locke. We will see the alternate timeline destroyed by the island's electromagnetism along with the entire world in one bright flash before everybody's eyes. And perhaps this reality is where Jacob comes from (but thinking about the logistics of that is like the compass debate, it is a mindbending riddle within a riddle.)
Either way, something very important HAS to come out of this alternate timeline that effects the original timeline in someway, otherwise there will be no point in the writers doing it. I believe from this cataclysmic event SOMETHING or SOMEONE will be effected in such a way that it changes the doom laden Flocke present day in a way that gives "the good guys" their advantage back. Alternate Timeline is redundant from a narrative storytelling point of view unless it EFFECTS things in a BIG way. If it's the last season I imagine it will.
So yeah, that's pretty much it. I've chimed in. Hope you enjoyed. Season 6 ain't far off now. Answers will finally arrive on our shores in a big gift wrapped magic box. Whose for a big box of Mr. Cluck's?