So the ingenious Season 5 Lost pitch is this: what if our heroes were jumping around in time like Billy Pilgrim? They could find out more about the backstory of the island, in all kinds of different time periods. They could see their past selves from previous seasons, as well as younger versions of other cast members.
Lost is very sensibly using the paradigm that doesn’t allow the time travelers to change the past, ever. (Except, for Desmond, who is special. If you are Scottish and say “bruither!” a lot you can change time.) There’s nothing you can do that wasn’t done, to paraphrase the Beatles.
Lost is often criticized for its gaping plot holes and dangling plot threads (to mix two different bad-sewing metaphors). But you know what I bet the show’s writers’ room is moaning right now? “Why, oh, why, didn’t we leave more dangling plot threads?” Consider: all kinds of mysteries from past seasons could now be explained as the actions of Future Juliet or Future Sawyer or somebody! Remember that time Charlie clocked Sun for no good reason? If they’d never revealed that as Charlie (it never went anywhere anyway), it could have been Future Locke somehow.
Think how cool that would be, to have a character step in and tie up some lingering plot thread from season 1 or 2. Viewers would (for a change) actually think, “Aha! They had this all figured out long ago!” Of course, they didn’t. But the illusion of competence is more important than actual competence sometimes.
But there are few such dangling threads, and now the writers are as hamstrung as the time travelers. They can’t affect the past either. When Future Sawyer sees Past Claire and Past Kate giving birth to Past Aaron, as he did last night, he just has to look soulfully from the foliage and then move on. Because we know he didn’t jump out and give newborn Aaron a cool nickname (“Easy there, umbilical!”) and hang out for a while. The time travelers can be the jungle whispers, and possibly the smoke monster, who knows. But that’s about it. Moral to TV showrunners: leave all kinds of unexplained hanky-panky in your early episodes! You may want to incorporate time travel later. I think this totally could have saved Back to You.