I initially thought the flash forwards represented one possible future based on the current course. Not written in stone, but fluid and able to be changed.

However, I am starting to think differently. I think that the flash forwards are set firmly in place, and we are really just getting the story filled in on how the losties came to this future destination. I think this season will take us through to the end of the story as to how they all came to be in the future flashes. And the final season will pick up with them having to get back to the island and set things right.