D + P ( T + C) = J
Desmond in full Power, which is to say, once he has Control over his Timetraveling, will eventually become Jacob.
Jacob is on an Island which travels through Time/Space. Jacob is in a cabin which travels around the Island in Time/Space. Apparently, Jacob is the defacto leader of The Others and he's, through them, attempting to avoid a terrible outcome of a predetermined event . Attempting to influence that outcome.
Desmond has gradually grown to understand and be confident in his power. He was told by Eloise Hawking that if he didn't go to the Island, press the button for those 3 years, and eventually turn the failsafe key that "every single one of us is dead." What if, instead of the importance of pushing the button, she was refering to the impowerment of Desmond by turning the key? That without what Desmond would become, "every single one of us is dead." Faraday, assuming that Desmond is outside of the rules ( a Time Lord?), has changed time by interacting with the 'past' Desmond. This will eventually convince Desmond that, not only can Time be altered, but that he's the only one able to. He'll then spend the next few hundred (thousand?) years, traveling through Time/Space, attempting to influence an outcome.
Maybe Penny dies (mid Season 5 to mid Season 6) and she'll be the Loise Lane to Desmond's Superman. You know, when he flies around the world to turn back time?