There may be more candidates remaining than we think. We saw a special set of six associated with the numbers in the cave and in the lighthouse. To further reinforce their importance, Jacob gave Ilana a list of the "six remaining candidates" in her flashback in Ab Aeterno. Presumably those are the same six.
But we've been getting some hints that those may not be the only candidates. The main thing that I have been puzzling over is the fact that Ilana, despite having been given a list, still thought that Frank might have been a candidate. This seems to imply that there's still some more major players.
I propose that the following five people are candidates who Jacob has been cagey about, and may play an unexpectedly important role in the end game:
- Kate: was not crossed out at the Lighthouse
- Miles: appeared crossed out on the candidate list, but it's unclear why (he's still alive, he hasn't acted 'evil' on the island, and he isn't infected)
- Rose: appeared crossed out on the candidate list (Henderson), but it's unclear why
- Frank: Ilana asserted that he might be a candidate, even though she had a list that didn't have his name on it
- Desmond: seems to have a special relationship with the Island and is subject to "the Island isn't done with you"