A lot of people are worrying about the names on Jacobs cave (which no doubt is interesting) but I think a bigger question would be how the two timelines will come together. I'm hoping the timelines will allow us to see a happier ending for most of the characters that have died or been screwed on the island. For instance Boone and Shannon living happily after ever. Maybe Libby will return for Hurley. Claire will be reunited with her baby as well as with Charlie. I can't see of any other point of the alternate timeline merging with the real one besides making the story end on a good note and the sad things that happened on the island are somehow redeemed or taken back. I think that Desmond will be the one to tie the two timelines together though since hes the only character that can kind of travel in time.