More speculation on the vision quest: As I've said before, I didn't play the first game, so I don't know how old Altair was when he started, but Ezio was relatively young when he got pulled into the Assassin/Templar conflict. An interesting possibility for the start of the game is that we could be a young (half) Indian - whose parents are both dead - that recently became old enough to go on his vision quest. While he's on it, instead of the normal vision, where his spirit guide tells him what his role in the tribe will be, he's given a message from Those Who Came Before about the Assassin/Templar conflict in America and how he is meant to be a part of it. He returns to his tribe and tells the shaman what he saw, at which time the story of his parents (both assassins, maybe?) is revealed to him, and he begins his assassin training soon after.
A vision quest is actually done while you're still a kid, because that's when they start training you for your role in the tribe, so there would be an "X years later" sequence, similar to the fast forward from Ezio's birth to him being a young adult.
I was too focused on the Revolution story when I saw the leaked image. I'm much more interested now that I'm thinking of the possible Native American influence on the story.