So after "The Last Recruit", a very obvious answer occurred to me. Claire's scene with Jack over their father's will seemed a little random at first, but the result of this meeting is going to have a giant impact on the show. This reveals something I feel I should have figured out a long time ago, but am just now beginning to realize. The reason it was so important for Claire to raise Aaron is that time always MEANT for her to. It was her fate to raise him, and whatever timeline or reality we are in, the situation will make that so.
From season 1, we are shown how important this is- the crazy fortune teller guy who demands that Claire take that flight. Although he admitted he was a phony, I want to believe he had a moment of real cognition here, as his reaction was so strong even he seemed surprised by it. However, he is no time expert like Eloise, and probably believed it was his duty to get Claire to raise Aaron herself. As we now know, time will course correct itself- it doesn't need some washed up Cleo-dude meddling in its affairs. So his interference was unnecessary, and irrelevant.
If Claire had never met the fortune teller, and never gotten on flight 815, she would have tried to put her child up for adoption. It seems that the only thing stopping her was the plane crash, and the sudden need for her to step up and take responsibility. However, this is just a ruse. Do you remember the real reason Claire didn't want to keep her child?
She wasn't financially stable. Her boyfriend left her and she was too scared to raise a child alone. This is where destiny comes in.
Jack's dad had died, and presumably left Claire a good amount of money in his will. This would have reached her eventually, and she would suddenly have all the financial stability she needs to raise her kid. Not to mention she would have discovered her secret family in Jack Shephard, etc. offering her even more support. As we are now seeing in the alt-universe, this is probably how everything should have gone, had Desmond never been around to push the button- or more precisely, not push the button, and cause the plane crash. How suitable that he is the one who has to correct time now, with the alt-universe coming into being. We know from Daniel that he 'already' set off a nuclear bomb, not in the sense of time but progression of the show. It is strongly hinted that the alt we are seeing now was a timeline created after the plane-crash timeline, so this might possibly be a third or fourth reiteration, who knows.
The point is, I'm certain that Aaron isn't going to be some savior of the show, the next Jacob, whatever. The only reason he was built up to be so important was simply that Claire was meant to raise him, as that's how life would have worked out anyways. No matter how much interference Claire's life receives, be it Desmond or fortune-tellers or Kate or Smokey or financial issues, time will correct itself and keep them together.