Its a simple idea - When Hurley stumbled upon the cabin, and was staring in through the window, there was someone in the chair, but then someone popped up right next to the window and scared the hell out of him.
This was Hurley from the future-past? Hurley that was in Dharma?
Obviously, to be true, this would have to mean that the losties survived the incident and have been living on the island since, perhaps aging, perhaps not, and were possibly there when the plane originally crashed.
Fellow fans of WHH listen up. This could explain the rumours of ALT.
There is no second timeline. The time travellers could have left the island at any time in this 30 year gap. They could have all got on a plane together, even. And headed back to the real world while their past version of themselves where on the island.
1 more thinking point. Has Claire been travelling through time or not? It raises interesting points concerning specific rumours...