M, even with parallel realities and everything, I doubt any time related issues could shock us that much, after everything we've seen this season - Ben time travelling, Desmond doing the same, the time discrepancy between island and off the island. Also, the rteturn to another timeline would complete things to much, when would they end up, in a time before the plane crashed or in an alternate realities where their "official" self are dead or something like that?