[DAI Spoilers] [Dreadwolf Spoilers] My theory for DAD's plot

There's a theory that suggests the Golden/Black City, is really Arlathan, or a part of Arlathan at least. If this is true, Solas will be looking for a way in to complete his plan, and kill the mage gods imprisoned there. We'll need to find a way into the city ourselves. So our quest is to find a way inside, and how to avoid getting infected by the taint. Along the way, we learn more Tevinter's history, Elvehnan's history, how the Elven Mage Gods went bad, and are forced to make difficult decisions that all have benefits and drawbacks.

In the end, the PC, and Solas, enter the Black City. And we also encounter the Elven Mage Gods who reveal some more truth's that Solas was unaware of that make the whole thing a lot more messy in morality. It's here we get the final choice of the game. What the choice is though, I have no theories at the moment.