This is the most intriguing question of s6 in my oppinion.
Just before Jacob dies he says: They're coming.
This could just mean that hes talking about Ilana and Bram knocking at the front door of the statue but I think its a hint towards something more.
Who or what do you think Jacob is talking about?
Personally I think that hes talking about the folk that are stuck in 1977 that just zapp back as soon as the bomb is detonated.
- *(Therefore making it impossible for the Nemesis to win because the hatch will never be build, flight 815 will never crash and thus Jacob is still living in another timeline. S6 will be about the losties dealing with the nemesis). *
This is beside the question of subject of discussion, just a personal idea *