If it is true and the veil is torn with demons coming in, they would want to control the world. Can we side with them? Wud be interesting. Summoning demons to do ur bidding and ruling over the threatened population is appealing.
Btw, in the past there were some codexes with told about some demons being more powerful than pride demons. I wonder if such a demon will appear
Read The Masked Empire and you'll have a pretty clear answer to that question.
There are many individual demons stronger than generic pride demons, it is simply on average a Pride Demon is the most powerful type of demon (that we've yet encountered, since at least one new type is being added in DAI).
Given the evidence of past DA games: Jade Empire we can control Death's Hand and control the world through evil magic. KotOR we could control the Sith.
I'd say there's a fair chance we will have a similar 'be evil and gain control!' ending. I doubt that this ending would be importable to any future game as it would mark a distinct ending to the story (it's hard to recover from a full-blown Armageddon), but that doesn't mean the devs won't allow us to choose it anyway.