I don't think aliens play into it at all, although it would be awesome. I do, however, think that the island's ancient structures/technology (smoke monster, wheel, statue) is a remnant from an ancient civilization, not from the future. I mean, if it was all happening in the future as well as being perceived in the shows present time-line, it would create a classic unsolvable paradox; if an event occurs in the "future" and is subsequently transported into the "past", then how could it occur again the same way?
I mean, that's all fun theory but I'd be pissed if they chose an explanation like that for LOST.