My theory is based on how island life was extremely more challenging, emotionally and physically, and they grew stronger. Also, more aware and more intelligent. Each year, and then on into the FS., which I feel is a higher plane of existence created by the "Losties", who are now imbued with the power of the island. If I were to guess about a physical entity, representing the island, it would be Vincent. And I stand on my opinion., that Jack was healed and only later did Hurley and Ben take over the island. I can't quite see Jack going out like that. When, in the FS, kate said, "You don't know how long I've waited to see you", it sounded like a lot longer than a mere 70-80 years. What an ending! I'll never forget the powerful impact of "Lost" on my life, and am grateful for all the amazing people I've met here on the "Lostpedia" sight.