Now, we may not be satisfied with the way the writers are answering some of our questions, or the extraordinarily lazy ways they're resolving some of the major mysteries of the show (I know I'M not) but I gotta say... I think they had this all planned out.
By "this all" I mean the flash sideways. I mean Smokey taking over Locke. I mean all the major plot points of the narrative. Obviously certain characters like Ben and Eko became wild cards. But I'm betting the flash sideways idea was there from the beginning. And I'll tell you why.
Desmond's line when he first met Jack in the stadium. Remember? "See you in another life, brother."
That seems way too specific a piece of dialogue to have just been a cool saying. I think they knew way back then.