Since finishing Trespasser, I have been brainstorming about the story for the next game.
1. Have a weakend (no arm, level 1) Inquisitor carry over from Inquisition. This would make sense since Trespasser ends with a Inquisitor vs The Dread Egg thing. The Inquisitor not having the epic equipment can be handwaved by saying that they couldn't travel to Tevinter with epic stuff like that (i.e. too suspicious traveling to Tevinter with a armor of +200% golden awesomeness). The whole no arm thing could be fixed by having the weakend (level 1) Inquisitor running around for the first couple of hours looking for a badass ancient magic Tevinter prosthetic made out of Lyrium or something (this new arm could grant a new ability tree like the Inquisitor tree in DAI, like doing that lyrium hand-of-death thing that Fenris did in DA2).
2. New character. This is the most likely in my opinion. With the Inquisitor taking a mentor/advisor role for the new character. Think a combination of Morrigan and Hawke from Inquisition with information about the enemy, acting as an advisor, but more involved in the plot than either Hawke or Morrigan (like a war table advisor maybe?). The new character would be recruited by the old Inquisitor or someone related to the Inquisition (Josephine/Leliana/Cullen/Scout Harding/The Inquisitor/Dorian/Iron Bull?/Varric?) on the basis of their origin story and not being "corrupted"/recuited by Solas.
A human mage could be from a Tevinter magister family (exactly the kind of person who would oppose Solas, recuited by Dorians faction in the Magisterium).
A human warrior/rogue could be a Tevinter gladiator or criminal from Minrathous (not Solas type, no magic also human).
A gladiator Tevinter could be recuited by Harding/Cullen after seeing the gladiator in action in the arena fighting like a boss.
A criminal Tevinter could be recuited on the promise of money/"We need someone with your connections in Minrathous"/We will get you out of jail if you come work for us", getting recuited by Leliana/new spymaster/Inquisitor.
A dwarf could be working in the dwarven embassy/lyrium trade/carta in Minrathous (also not Solas type, no fade connection after all), getting recuited by Varric/Harding or Josephine with her diplomaticness.
A qunari could either be a Tal-Vasoth mercenary (we all know how Solas feels about the qunari after all), getting recuited by Iron Bull/Inquisitor (Tal-Vasoth mercenary angle similar to Inquisition or even a Ben-Hassrath agent sent to aid team anti-Solas, not likely though.)
A new elf character would also be interesting, since such a character could be a slave in Minrathous, who might even be sympathetic to Solas cause, but not willing to let the world burn (could be recuited on the basis of not knowing about Solas cause or even not having a chance to get "corrupted"/recuited by him, you know being a slave and all).
In all the cases above getting recuited to team anti-Solas could be something like DAO with the player getting recuited by a Duncan-like character (Inquisitor/Inquisitor's friends/random middle man). I would be fine with the Inquisitor having a Ben Kenobi like role in the story as a mentor/advisor. Personally I think either a new character or continue playing the Inquisitor (Mass Effect-style) would be fine. Also I personally would really like to play a good (or an evil blood magic one) Tevinter magister (swaggering around Minrathous with Dorian). It would be fun to play as the good (or typical) Tevinter. Also playing a Tevinter who fights against Solas and his elves attempts to destroy the world, would have a aspect of history repeating it self to it (Maybe even harnassing the power of old Tevinter to do the whole Tevinter vs the Elves again).
Sorry for long rambling post btw needed to get these ideas out my system afte Trespasser.