Well, we know most of what we've been these past two years was intended to be in the base game, although it's surely gone through some changes while in development to fit the edited launch story. I try to see it like this: the two years of destiny we've had is a much smaller time-frame in the game. Maybe a few months, not two years. Might be wrong but I'm thinking they're side-quests while the actual story unfolds in the future