I got another idea, the Vex are going back in time to reverse what happened in vanilla Destiny. You are sent back as well to try and stop them, getting to partake in epic battles like Twilight Gap, the Raid on the Moon and the Reef Wars only that the Vex are now involved in it. For dlc (if this was a separate game) it would add on other battles that we may not have even known about. I think that that makes for a pretty good game. It would help to fill in some of the backstory on these battles and get to see it in action.