I think it should revolve around a war between the Carja and the Quen.
In HFW we know that the Quen's Homeland is being desimated by the blight. I think that the Quen would ultimately abandon their mission to save their home after the expidetion takes too long. They would decide to just colonize North America. This is where they'd have to fight the Carja. I imagine Nemesis using the Carja to kill some opposition. The war between Carja and the Quen takes place in the clan lands of the Tenakth. This means we explore the Forbidden West map again, but now it's war torn. There's huge Carja forts everywhere, most likely big battles between the two, and probally hostile Tenakth. I imagine the Quen and Carja outposts would both have tortured Tenakth captives we can free too. Aloy would also go East, North, and South to find many new lands and tribes, while also exploring more of the ZD map.
