I think Jason suggested something like this around the time of the premiere, but the more I think about it, the more I like it:
http://theoriesonlost.blogspot.com/2010/02/how-lost-ends-expanded-theory-by.html
Given that the last two weeks have had moments that really feel like character closure (Locke off-island accepting the things he cannot change, Jack making sure that he doesn't repeat the mistakes his father made with his son), I'm kind of buying into the thought that the flash sideways are, in fact, the end of the show (or at least a "Return of the King" style denoument for the characters). The timelines are more or less parallel, but as a result of what happens at the end of the show, and not the finale of last season. When Juliet tells Sawyer "it worked", she's wrong. She gets a glimpse of the alternate timeline, yes, but that comes about not as a result of Jughead exploding (Jughead might turn out to be the failsafe at the Swan Station), but whatever sinks the island at the end of the show. The more they try to emphasize link the reset to around the same time as the Incident (like Jack's appendix), the more I think they're attempting to throw us off.
Of course, as with anything related to the show, this could be completely wrong.