This is definitely me being a completely selfish Solace-Levallan player, but man the idea that perhaps the Black City could be Arlathan is making my Pro Inquisitor PC brain itch.
The revelation that the Tevinter Imperium did not destroy the Ancient Elves (the Elves destroyed themselves), the Imperium was merely scavengers. Combined with Corypheus' insistence that he "Found Only Chaos and Corruption, Dead Whispers" and the whole "The People fell for what I did to strike the Evenuris Down, but still some hope remains for their restoration. I will save the Elven people, even if that means this world must die ... I am not Corypheus, I take no joy in this, but the return of my people means the end of yours" from Solas thing and there is some serious weirdness here. Lastly there is Abelas when a Dalish Inquisitor asks him to help the Dalish learn about their past, he responds "Our" People? The Ones we see in the forest, shadows wearing Vallaslin? You are NOT my people."
If Solas still has no intention of saving his own love interest from the cataclysm caused by the disappearance of the Viel then it is highly doubtful that he intends to save any of the "Elves" of current Thedas. If anything, like Abelas, he does not consider them truly "Elvhen" and therefore not "his people". Who then is he going have return or save? Combine this with the fact that both these Ancient Elves have admitted to waking from a long sleep ... then perhaps both of them are still inflicted by the disconnection of he Fade as well; and thus still aging. Simply, the hibernation allows them some level of longevity (going to sleep connects those with magic closer to the Fade after all and it is this disconnection that is a cause of Ancient Elves to begin aging).
"The Black City" is always at the center of the Fade and no matter where you enter you are always equal distance from it, perhaps that is where Solas created the Viel? Could the entire city been have made into the prison for the Evenuris? If so, since "Arlathan" was the Capital CITY of the Ancient Elves maybe ... just maybe, there remains a large population of Ancient Elves trapped there with their "Gods" and since they would have never been removed from the Fade they would still retain their Immortality.
Then of course there are the Codex's that Arlathan was once in what is now Tevinter ... maybe it was before the creation of Veil? Which would bring the Tevinter as a setting into play for sure. What would happen if the Veil was brought down and Arlathan returned to its proper location and that location happened to be on the strangely isolated island where Minrathous happens to be? Marvelous!
Finally there is one (perhaps throwaway) line that Cory says to the Inquisitor that always sticks in my brain whenever I hear it. "I will not suffer even an unknowing rival". What a weird thing for him to say, because a person who is trying to thwart the Breach (and only subsequently him) isn't a rival even if they are using the anchor, they are an enemy or a hindrance. The term rival literally means "A person or thing competing with another for the same objective", but Corypheus' objective was to go into the Fade and become a God and he probably knew damn well that wasn't the Quizzy's intent. Well then an "Unknowing Rival" literally would be a person who has the same end goal (or at least the potential for the same end goal), but doesn't know it? Even Solas makes fun of you for being a considered some sort of "Demi-God" in his first companion dialogue and gets mad you in the "Punching" scene about playing at something equivalent to a God. MY CONSPIRACY THEORIES ARE GOING OFF THE CHARTS FOLKS!!!! ALL HAIL INQUISITOR GOD!!!
And people say there aren't enough interesting tales to tell about a PC Inquisitor for Dragon Age 4. 