One thought for Door #5: if it somehow included the notion that the 815 crash that Widmore elaborately "faked" was an authentic Flight 815 after all, with everyone onboard (all the characters in one of the realities) dying, that could be pretty cool, depending on how it's handled.
Not according to the producers. Lindelof and Cuse have said unambiguously that the flash sideways are not an alternate timeline in any sense, and the characters are the same characters.
Did they say timeline and not reality? If so, that could be an important distinction.
And the pilot corpse without the wedding ring Frank saw on TV was in fact him? Creepy...