Here's my idea for the next DLC: The starting mission has you go into the warmind mine and secure the intel from Cabal. At the end of the mine, a mysterious Vexified-Warlock will appear similar to how Vex spawn and knock your guardian back as he takes the warmind's intel. You are giving more quests on Vex anomalies until you find out that the leader of them, and the Vexified-Warlock, is Osiris, the Speaker's old apprentice. You are then tasked to go to Mercury and reconstruct an ancient Vex portal, allowing transportation to the Vex's realm where you try to save Osiris but end up killing him. The raid of the DLC will before Osiris dies, he creates a Hydra to take his position as the Vex leader.