Which would tie into the north American empire that the cyptarch alludes to. Destiny is most definitely about the time stream and the ability to move to and from present past and future. The stranger is most definitely using vex technology to move through space and time which should be expanded upon so I think in addition to your well thought out idea that the environment should be phased meaning that if you complete a task for you and all others that have completed it, it would change the environment eg: World of Warcraft: Wrath of the Lich King forward. Going back to the time notion the title of the game is Destiny so I think in some far flung DLC a player should be able to save the past "pre collapse" in order to change our present in the game