We might actually be going that route if what I said about the Grey Wardens and their killing of Old Gods is true. The Elderscrolls does this to an extent, so it's possible Bioware could take this approach. They didn't mind taking a popular religious theme and challenging everything you believe. I never thought they'd have the balls to tackle belief in this game, but they did and I love that the most about Inquisition.
I fear I am not familiar with your theory.
However, I also fear that the second bit was lost on me. I never felt anything I had believed in to be challenged. The Maker is not challenged, the gods aren't either. The mark not being Divine sent did not surprise me because I refused the Herald thingy from the start. The vallaslin did not surprise me because I, Siha, always refused to have them because all my knowledge (before Giton posted that one bit about an African tribe) of facial markings implied they meant something bad. So for me no faith was shaken, unfortunately. But for all who the game did show this to: it's cool and I envy you.
Reven is probably the closest BW has come to making the PC an antagonist. The idea would make an interesting game especially if it starts with all the usual RPG trappings of a hero's story like being recruited, finding companions etc.
My problem with Reven is that she is, after all, the hero (or villian, if she chooses to be). What they revealed is in the past, not related to her current incarnation. So this does not really count so much for me. It was a nice twist, but it is not exactly the same Taelaa mentioned.
Why does Solas disapprove of the Grey Wardens method of killing the Old Gods?
I've heard something about the pantheons being related to the Old Gods (not sure about that theory)
How else can you end the blight without killing the archdemon? What does he expect people to do?
I think the method you mean is the demon army? Well, Solas just doesn't like the demon army. The devil that we know.... you know? Unleashing a demon army, a potentially greater evil that nobody knows anything about and that cannot be controlled? Too dangerous, too stupid.
So I think at least.