Here, here, to that! In a way that is what happened in ME2, the Reapers were still a threat but they were working through puppets, so you were working one step removed from the main enemy. I loved the game and the ending but it set things up for the final showdown in ME3, plus a proper explanation of why they were acting in the way they did, although in ME1 Sovereign did say that they were above giving explanations. In the end the justification was very shallow, particularly if you had in fact succeeded in uniting the entire galaxy against them because it actually refuted their main assertion as to why it was necessary.
The trouble about going off to Tevinter if it isn't going to feature directly in the Solas plot, is that you are always going to have in the back of your mind, when are we getting back to dealing with Solas? Of course your PC may well not know the imperative of this, so role playing them, they are not going to have the same sense of urgency, unless of course someone tells them. I'm hoping that something about Tevinter and its history is going to be very important in the grand scheme of things.
I certainly want to know a bit more of why Solas has acted in the way he has. I was annoyed at being asked to make a decision about how the Inquisitor responded to his reveal of his plans, when I had so little information. On the face of it I needed to stop him. How was I going to "prove him wrong" when I had no way of knowing what exactly he required by virtue of proof? It would have been helpful if he had answered the question "Why does this world have to die?" The fact that he didn't and even said that would help me too much, seems to suggest that it is the crux of the whole problem. So it will be intensely annoying to still be left hanging about it at the end of the next game.
You will recall that in ME2 there was a suggestion at something peculiar going in in a certain star system which seemed to suggest a sort of energy drain. This was never elaborated on and some people have suggested that was going to be the original reason for the Reapers that was later altered to the one given. Whether that was true or not, I hope that the plot remains true to the original vision for DAI because hopefully it will have some sort of internal consistency. Things do tend to fall apart and not make sense if you change course through making it up as you go along, rather than having an overarching plot which you are working within and has always had its internal logic from day 1.