1) The nuclear explosion causes an alternate timeline, that exists next to the original timeline. Eventually the two timelines will string together in some way
2) The two forces that are going up against each other are Those who belive in "Fate", and those who belive in "free will". WHH with the ability to change time, The Constant Vs The variable, Destiny Vs Choice.
3) Aaron is Jacob's Great Great Grandson... No proof of that, but it would still be cool.
4) The real Aaron died during the 815 crash, (Because Claire couldn't feel the baby), and then Faaron takes it's place (Because he suddenly starts kicking again). He then grows up to be scary dude at the end of S5. It might be a bit lame, but i'd like it !
5) Finally, a giant asteroid crashes on Earth, and it then turns out to be the island (Again, a bit lame, but i still think it would be okay)
What do you lot think ? (Note: Most of these theories aren't mine)