The Island may very well be the Halls of Ma'at!!!!!
I absolutely love that theory. I have kinda always liked the (underworld) or not purgatory, but something kinda like it theory.
I remember seeing Richard Alpert for the first time and always thought, "Man he looks like he is wearing eyeliner". Maybe the casting was done specifically for that roll. Maybe Richard Alpert is "Modern day Anubis" That’s why he never ages.
Plus it Makes sense why Oceanic 6 or 5 (since Aaron doesn't really count with this theory) had to return to the island. To be judged. So they could be reincarnated.
I don't think we have seen the last of the "time loops" I think there will be another to put them in a time that will coincide with them being reincarnated and course correcting itself.
Picture this, End of lost time has finally course corrected, they are all on the plane, and it never crashes. They get to there destination, All of them smiling and happy, then Boom … LOST