So I had this idea earlier. So storylines with the Vex and time traveling. Yeah been there, done that. BUT. What if we have a story that starts off with the Vex somehow almost wiping us out. First few missions are humanity getting kicked in the teeth. But then someone (Exo Stranger or someone new maybe) finds a way to send us to the past to find an object that will help save us. And the time we go back to would be before the fall. So we see the world in it's glory. Now to make those missions interesting have some Vex chase us to the past.
Only issue is figuring out how the devs would want to handle the time travel. Would it be like Avengers Endgame? Or Back to the Future? Or something else?