All the way through Lost, there have been un-explained visions. Some have simple resolutions (like Dave) but others are nearly impossible (like Locke's visions). From a Sci-Fi point of view, I think I can explain the latter.
Ok. So Sawyer and Juliet have lengthened The Truce. If this continues, then with their knowledge the Losties can shut down the Tempest before the Purge even occurs. That means that DHARMA will continue working on the island, and most of the deaths of the Losties won't occur!
My proposal is that these visions are images of the people in this newly created alternate time-line, their images pushed into ours so that the characters in our timeline will find their way back and stop the purge!
Any thoughts?