So we know it involves the Dregens and the Cabal. Currently, there are two cabal faction (3 if you included the remnants of the Red Legion). That is Caitals Ascendancy and the Shadow Legion. The Shadow Legion without Calus, the Witness, or the Echo of Control are directionless, Mindless slaves (Bungies attempt at making it so they don’t have to include a bunch of Cabal Characters). So, what if an incredibly powerful Lightbearer, one capable of wielding the Darkness to an extreme efficacy, so much so as to create a Weapon of Sorrow without the usage of Eris and her Hive Magic, were to start controlling the Shadow Legion. You’d essentially have the Empire and Darth Vader/Palpatine.