I would have to disagree with this! Just because we aren't getting an 'expansion', doesn't mean we won't be getting major story content. Bioware always has had a habit of having DLC with fairly huge consequences on the next few games. Corypheus, for example, came as a result of DLC. Then you have Lair of the Shadow Broker and Levithan for Mass Effect.
Yes, but they are all stand-alones. Corypheus was basically a set-up for the next game, he had nothing to do with DA2 itself. I can't speak about ME because I haven't played it past 1, though, but my understanding is a different team made them, for the most part.
The biggest reason why I don't think there will a Solas-heavy DLC is because somebody from Bioware had said there would be no Awakening-style expansions and DLC would be focused on new areas with contained stories. Obviously, it was a few months back, but it seems legit. Also, the elven gods stuff seems to be too big of an event to be resolved in a DLC. There was just too much set-up in Solas' character and the endgame with Temple of Mythal.
I do think it's possible to get a Witch-Hunt like coda (but without a happy ending, because I really don't believe there could be a happy ending before Solas' mission is resolved in any way, it would just be very inconvenient from the technical standpoint). But I'm not sure how exciting it would be for the majority of players. Morrigan got her DLC because she was a much more marketed character who had a lot of fans. I'm sure 20 times more people romanced her than Solas, and even those who haven't were at least interested in her. For Solas, of course, there are fans, and many people enjoyed the romance, but there are lots of people who basically haven't even noticed him. There are very different reactions. While I think the reception overall is good enough to give the romance a belated happy ending in the next installment, I'm not sure the producers would consider the character himself popular enough to get a DLC just about him.
I'd love to be proven wrong, of course. I seriously want the Inquisitor, any Inquisitor, to learn the truth and have an opportunity to react to it. The narrative logic just demands it. Plus, there's the unresolved thing with the Fade hand, which technically is connected to Solas, too.