I was thinking about the role of Jack (despite not liking him very much, I think he will have a big part to play in the next season) and then I remembered Ilana talking about Frank being a candidate. A Candidate to what?
Since Jacob is (presumably) dead, perhaps a new Jacob is needed (to fight Nemesis?). Then it came to me that Jack and Jacob are related names. I did some research and found (you can go to wikipedia if you wannt) :
"Jack" came from "Jakke" which was related to the name "Jan" (John) or "Jehan." All these possibly came from the French "Jacques," which relates to the names James and Jacob.
So, maybe JACK is going to be the new Jacob? Or Sawyer?