Looking at the lore which dropped in WQ, we can guess that we will have a season focused around Rasputin, a season around Calus's return, and a season about Erimis. My prediction is S17 will focus on us teaming up with Anna and Mithrax to enter Rasputins mindscape. There we will work to remove the Witness corruption and rebuild his mind. Meanwhile as the season progresses we will see Anna make progress on Rasputins physical exo body and the season will end with Rasputin being upload into the body. Also I predict we will see Arc 3.0 in S17 given the mind spear was a taste of arc 3.0, and skip grenades were nerfed. Also trespasser is arc and we know that will return. The dungeon that will launch will have us clear the warmind bunker under shaxxs castle. S18 we will see Calus return as a disciple along with the leviathan and we will manage to kill him with the aid of Mara and Ciatal. Ciatal may die and come back as the 1st cabal guardian. S19 the Witness will revive Erimis and she will become the next disciple. She will then lead the Witness forces on an assault of the last city as part of light fall.