Personally I think it would be cool to do something along the lines of... "In his death throes oryx attempts to TAKE one of the guardians that killed him. However due to 'whatever reasons may fit with the existing lore' the guardian is bestowed with power instead of being summoned to the shade..." or maybe a mini quest line like the new subclasses in ttk... This resulting in some hybrid Taken gaurdians of the light. I just think since it takes void, solar, and arc to fight the dark...the darkness would be a thing eventually harnessed in some way by the guardians, just like they did with the first 3. Just a thought.