Ok this is a really crazy theory but i think it might happen. Put your spinfoil hats on. The prophecy from the house of rain said there would be one creature to unite all the fallen and become the kell of kells. Skolas intended to fulfill that prophecy but we stopped him and killed him. The prophecy has yet to be fulfilled.. What if the Guardian, THE PLAYER, will be the kell of kells? The game is called DESTINY after all, and fulfilling a prophecy is fulfilling a destiny. This could really be what bungie intends to do with the story. The lore shows that the fallen arent really bad or dark, they want the traveler just like we do. If the guardian united the houses and became the kell of kells, the combined force of the Eliksni and the Guardians might be enough to destroy the darkness. Plus they could add eliksni as a playable class later on. Just something to think about.. Edit 1: Also it has been clearly shown that a kell doesnt have to be eliksni, since mara sov was the wolf kell for a while