Cabol would only be in limited areas, so the older parts of the game can stay the same. With some modifications of course. A new crota rises on the moon ? A new mini atheon rises on venus? Simalar but different new playable areas ? Great potential exists here! Could even bring back some favorite guns for speacial aplications. This isn't really that hard to come up with story here.

Yep, and Vex would be ok