What does seem apparent is that the world is going to change in some way. Flemeth goes on and on about it. We have prophecies like the one of Sandal or dreams of Leliana. Some could say that this could have been dropped, but I don't think it is - not with current reveals and not with Flemeth basically marching to Inquisitor, whom she can declare that they're basically the "herald of the new age", while OGB Kieran calls his mother "Inheritor" who awaits that age.
We know nothing of Morrigan being immortal, and the whole 'herald' thing (and titles like First-Thaw - funny title for some, but Svarah eloquently explains that it's one that means "when the ice breaks and new spring comes to give life to the world") reeks of this whole change thing being imminent and therefore tied strongly with either Solas's plans or whatever comes right after him.
That hinting would be pretty anticlimactic if we just end up playing as someone else in DA4, and they usher in a new age instead, in my opinion. If the plot was cut in half, I'd really like to play the second half as the character that plot was intended for 
Oh, it's Ok, I already committed racial genocide by picking Destroy option in ME 3. I guess it is too late for me to turn to the light now.))
High five 
Yeah, I have strong feelings about that particular choice.
Absolutely. And now I am returning to endangering the world and ripping... whatever I am ripping... (gosh, so many evil things on my mind, I really get confused sometimes).
Ah! Got it! Returning to the topic, I am really curious to see what exactly developers have in mind for us regarding Solas plan. They kept it so vague (deliberately, of course) it is really hard to figure out. It might affect how we view Solas, too. I just hope it will not involve red/green/blue buttons...
I can see it now.
Green: Remove the veil and merge the material and the fade! Mortals and spirits become one... Somehow 
Blue: Strengthen the veil, Qunari style! Everyone becomes tranquil, sucker!
Red: Kill Solas, retain the status quo, but all spirits die because reasons.
Bonus Yellow option (added in DLC): Defy Solas, but don't actually make a decision! Everyone dies, you lose and Bioware hates you!
Or something like that 
Yes, I agree, there it will be changes, too much foreshadowing for them not to come. (Or Bioware will get a golden medal for trolling on the epic scale.) On one side I hope it will be something massive (and we'll have a good variations of ending choice with all shades from Doom to All! to Perfect World - of different types since everybody's idea of perfection is different), but then, I guess, they'll have to end the series... and I really like them, so I am very torn....))
Well, they wouldn't have to end the series. They could always just set the next game in another galaxy...

This would be the same as if he said, "What if McDonald's didn't serve cheeseburgers, but... [served tacos instead?]" Which would imply that McDonald's does currently serve cheeseburgers. This is currently, mind, not during Solas's previous time.
Then the game mechanics get in the way of storytelling. After the encounter with Corypheus, the Inquisitor is thrown into a cave where they come upon some demons; we get a small tutorial that explains our new ability and we can use it from then onward. But what is supposed to be the story reason for that? Was it instinct? Intuition? How did the Inquisitor suddenly know how to do this?
I've always found the Adamant scenes to be similarly odd. When the party is falling into the canyon, the Inquisitor extends their arm and opens a rift as they are falling. Was this instinct that only came through in this emergency situation? Later on, after coming back through the rift, the Inquisitor closes it with a simple closing of the fist, seemingly with more new knowledge of how to control and use the Anchor. The expression on their face seems to support this. Is that really the case? Nothing is ever mentioned about it, which is pretty disappointing. Being able to open and close rifts at will should be a huge deal.
1. That is what the world could be, if McDonald's served tacos! That is what was lost!
2. Yeah, I've always interpreted it as a combination of instinct and the Inquisitor getting more practice with the Anchor as the game goes, even if it's subconscious. Part of the reason is that Quizzy develops more techniques with it when in great danger (no weapons, freezing to death in a cave with demons, falling into an abyss, etc.). It is unfortunate that is isn't explained or discussed though...