I think it would be really awesome if Bungie added in a sandbox feature. You could adjust ability charge time, duration, damage resistance, movement speed, etc. You could also add in any enemies, including bosses (not raid bosses). This could be on crucible maps or in certain parts of worlds. In order to have it make sense it could just be called the holo-program or something. There are already "meditations" where you can replay story missions. Ikora could run it. What you think?