Okay, so it appears this concert that Daniel Faraday is hosting and where David is playing will be a central point in the finale. Who knew this minor thing mentioned in Happily Ever After would be important? So here's who we know is attending.
Jack, David, Claire, David's Mother - My guess is Juliet, Sayid, Desmond, Kate, Hurley, (Maybe Libby for a date), Widmore, Eloise, Penny, Miles, Pierre, Charlie, and Charlotte. Possibly Sawyer if Miles makes him. I hope that somehow Ben, Alex, and Danielle end up going.
So here's what I think will happen. Daniel will end up with Charlotte. David and Daniel will have a paino face off sort of thing. (I hope that Claire goes into labor and the last scene of the FST is Aaron being born, but I don't remember how many months pregnant she was in the FST.) Charlie and Claire will end up together. There's got to be more plot related stuff like them seeing the OT etc.
So what do you think will go down at the concert?