I believe I understand what has happened to Juliet. Let me start with the season 5 finale. Juliet falls into the big tunnel thing and lands at the base. But let’s think about this; she is right next to the pocket of electro-magnetic energy. Another person this happened to was Desmond when he turned the failsafe key. This had a profound effect on him. He began to have premonitions, and later had the condition of temporal displacement. Temporal displacement causes its victims to have their consciousnesses being unstuck in time. Desmond began to flash between times. I now believe this has happened to Juliet.
After the bomb exploded, Juliet found herself trapped under the rubble. She screamed for help, and was heard. Sawyer and company struggled to dig her out. But if you listen carefully, Sawyer later asks is anyone had heard her since they started digging. Kate says no and suggests that she is probably just resting. Now stop. Why is this line said? Is it just for mindless dialogue? I believe this is significant. Juliet has temporal displacement because of the electro-magnetism. She has just flashed out of consciousness. She is at another time. Remember what Desmond was like when he was at another time? Totally out of it in the blink of an eye. So now, we have three questions: Where is Juliet, when is Juliet, and most importantly, in which timeline is Juliet? More on that later, what is important is that she returns. Sawyer finds her and talks to her before she “dies”. In this scene she talks absolute nonsense. She says something about getting coffee and “going Dutch”. What is she talking about? Something in her flash. Something made her think about coffee and Dutch stuff. She saw something. She was going to say something very important… and then she flashed away. Went limp. Gone.
And we know what happens now. Juliet is buried, presumably dead. But what if she isn’t? Can the Losties have done it again? Buried someone alive? I don’t know. Later Miles goes and tries to communicate with Juliet. He shakes violently and says, “It worked”. Juliet has realized somehow what has happened. There are two timelines, don’t ask me how, and I think she knows it. She is trying to say that their plan worked, which it kind of did. The plane landed in LAX.
Now for the part I’m kind of guessing about. I think maybe Juliet’s other consciousness is in the alternate timeline in which the plane lands in Los Angeles. But she remembers everything that has happened. She is the only person in that timeline that knows what has happened. And she will be the one who unites them. She will unite Jack, Sawyer, Kate, Hurley, Sayid, and the rest of them.
Now this theory does have holes. We have no evidence that Juliet’s consciousness can survive in any form now that she has been buried. But I believe this is the Juliet story. This is her random mumblings, her oddly sudden, poorly timed “death”. This is how the alternate timeline can get pulled together in some way. Juliet is afflicted with temporal displacement.