I don't think you can make a series by stretching out the reveals and plots. That's just no way to go. You need to pull out the stops for each installment.
I'd like to point out though that the original plans for Dragon Age wasn't that it'd be a continous series, but that it would be a set of games that had little to nothing to do with eachother plotwise, but were simply set in the same world.
We see this in Dragon Age 2, the game that might have 2 in the title, but isn't really a sequel. A game where the events have little to do with the actual plot of Origins, but merely use the world itself.
In games like that, you can have something presented in an earlier game as world building and not use it again until much, much later where it becomes a central plot of the game. The golden city is a contested example in this case, but another is the qunari. We've heard a lot about them ever since the first game, but we've yet to have a game that actually takes place in the heart of it.
And if they reveal that the chantry is based on lies what ever PC we have in another game will be biased since we know the truth. and the only way you could work something like that into the story would be to eliminate choice that the whole world finds out so our later PC wont be biased because of our out of game knowledge.
My pet theory is that they will introduce the Maker as a very powerful spirit. Something that can make the opponents of the Chantry say "See? He's not a god!" while the advocates go "what are you babbling about? He's still the creator of Thedas!"
Because mysteries are meant to be solved. Not solving a mystery is a failure and pointless. Stories are all about answering questions.
Not always. The Reapers from Mass Effect as an example that sometimes, the mystery itself is what makes the story so much fun. And solving it only takes away from it.