Before season of the Haunted, caiatl spoke of Eris in the dialogue of the psiops battlegrounds. Before season of the Plunder, Eris sent a message to Rat, Drifter, who was in the reef doing who knows what. If the pattern holds then Osiris will be the focus of next season as he is being mentioned now in the new lore. Currently Osiris's mind is being melded with Savathun's. I believe the next season will take place entirely in the mindscape of Osiris. Most likely there will be lot of vex as Osiris was always obsessed with them. Our job is to purge psykic projections of Savathun in Osiris's mind. The new dungeon will probably be another mind heist. Enter the mindscape of Savathun using Osiris as a link. Steal any knowledge Savathun has on the Witness. The season will end with Osiris rising again like the Phoenix of legend.