I think the foreshadowing has already been put in place to connect the Shephards, esp. Jack, and Jacob. First of all, Jacob has to be connected to the Shephards somehow b/c Christian and Claire use his cabin as a place of refuge. Jacob would not allow just anyone to "live" in there unless they were connected to him in a unique way. Also, throughout the duration of the show, only two characters are continually called "Great Men": Jack and Jacob. I can't exactly pinpoint all the occurrences, but in the episode where the backstory of Jack's tattoos are told, the woman tells him he is a great man. I think Christian refers to Jack as a great man when he and Sawyer meet in the bar in Australia. The first time Ben talks about Jacob, he refers to him as a great man. The same also happens when Mikhail talks about Jacob in Season 3 episode "Enter 77". Therefore, Jacob and Jack are SOMEHOW connected; at least from my point of view. Whether they are father/son, who knows. I know there is a debate about whether Jack and Kate "know" about Jacob, so why would they name their son the same as the leader of the others. I really don't know, but I think they have some sort of clue about Jacob, but can't actually remember for sure. But if they are not father/son, could they be, MAYBE, twins? Just throwing that one out there, but it does look like the signs are leading to them being father/son.