What if the place where Solas is headed after the end of the game is the Black City? What if that is the place where the elvhen gods have been imprisoned? In Here Lies the Abyss, if you take Solas with you he's all enthusiastically gushing about the Fade in general, and then he squees and goes "There's the Black City, it's almost close enough to touch." The excitement in his voice is pretty hard to miss. Then, later, after I finished Wicked Eyes and Wicked Hearts, I spoke with Morrigan and I asked her why she thought Corypheus considered me to be a rival. She then said, "Well, it depends...if you could go to the Black City, would you?" You have a lot of options to respond from "HELLLLS NAW" to "OOOOOH YEAH". I went the "OOOOOH YEAH" route, and Morrigan said, "Well, then there's your answer. You ARE his rival."
SOOO the Inquisitor has the anchor, which she can apparently use to open a door into the Fade that she can physically pass through at any time. It does not seem that she can open a door to get out of the Fade using the anchor (otherwise, in Here Lies the Abyss, she'd just open a door and pop right back out instead of traveling to the other rift). So she can open a one-way physical door into the Fade, which is what you'd need to do to get to the Black City.
In my head, I'm thinking that a trip to the Black City, one where you meet Solas (either on the way or once you get there) and get some closure, would be the perfect size for some DLC. It's basically one location, it's not super expansive, and it's kind of a coherent story. I could easily see this being like, the last DLC released before DA4. The inquisitor travels to the Black City, gets closure from Solas, and potentially either releases the elvhen gods or finds out what's really going on in the Black City; and all of that sets up Thedas for some crazy world-changing shizz for the next game. Personally, I think this would be AWESOMETASTIC.