“19. Amidst the chaos, the forgotten one cried, “When the last star fades, the emperor’s crown will weigh heavy with the sins of a thousand years.” The stalwart soldiers threw down their spears and wept tears of blood and burning anger.” - Song of Renilash
“The golden one claims a vacant throne. The crown of light will bring only darkness.” - Il’gynoth
Denathrius is possibly the Emperor of the Arathi and seeks the throne of the Realms of Light.
That last star that will fade? Beledar which is infact the leader of the Pantheon of Light? The reason for Beledar shifting to Shadow? I suspect that Beledar is infact Remornia whom Denathrius bound to his Sword after luring her defenses away from her using Lothraxion.
Remornia in order to hide her service to Denathrius orders a retaliatory strike against the Nathrezim’s Ward turning it into the Ember Ward.
After Denathrius is imprisoned he takes advantage of the Void Entities that the Nathrezim designed to consume Sins and has Remornia stab each one so that Denathrius can harvest each one.
The final one will be Ansurek(filled with Wrath after Xal’atath gives her the broken Dark Heart) which will be followed by Denathrius hoarding the Light and abandoning Remornia while giving a mocking echo of her decree: “There can be no truck with the Shadow”.
His goal is infact to bring all of existence under the sway of the Jailer so why wouldn’t he seek to hijack the Cosmic Realm of Light!?
If the Jailer falls he can simply take the Jailer’s place at the top!
The Pantheon of Light retaliated against Revendreth due to whatever event caused them to purify Lothraxion into a being of the Light(I suspect he used Lothraxion to distract them from him binding the Light’s ruler Remornia/Beledar to his Sword putting him in control over the Pantheon of Light) yet regardless the Enemy Infiltration Preface says that the Naaru will believe anything someone converted to the Light tells them therefore Denathrius if he usurps Beledar will become the God of Light the Naaru follow blindly!
Beledar/Remornia will be abandoned and need the Sacred Flame to purify her restoring her Day and Night Cycle. The Night Cycle will of course be due to needing the Dark Heart(which has Galakrond’s Hunger) to hold the Shadow though with it broken it can’t hold it for long and thus Light and Shadow will switch places(Light in the Dark Heart and Shadow in Remornia/Beledar at Night and Shadow in the Dark Heart and Light in Remornia at Day)
Of course the Sacred Flame is Arcane Holy Light so Azshara will make a grab at that to become a 2nd member of the Pantheon of Light while offering up her own Arcane to the Dark Heart in it’s Place making it so that Dalaran’s Arcane is what starts leaking out and gets grabbed by Remornia/Beledar. Day thus changes to Arcane Purple similar looking to Night’s Void Purple except brighter.
This is my theory at least.