The Inquisitor was uninvolved with Corypheus until they got dragged into it. The new protagonist will probably get dragged into Solas' plans somehow. And the Inquisitor will still be fighting Solas, we'll just be acting as their proxy if the ending of Tresspasser is any indication. And Solas' will be using pawns of his own. This battle has just shifted to a fight between chessmasters (Not to say the new protagonist will knowingly performing this role or can't reject it). I'm quite attracted to the idea actually.
I've already said why it has to be the inquisitor. It absolutely has to be.
I don't frankly care what they decided some ten or so years ago, about characters only getting 1 game, and any loose ends after that game are **** out of luck. Who cares about emotional closure for these characters, who cares if they have dangling threads hanging over your heads, who cares about whatever sequel bait we give you using said character. Any and all loose ends we may or may not acknowledge about said characters are irrelevant because "Thedas is the character" (which does not really say anything, or even really justify's why characters only get 1 whole game). All the characters do is clean up the mess the last one left, and by the time there done, there is juuuuust enough time left for THEM to make their own mess so the NEXT guy has something to clean up for the next 2/3 of the next game. It is frankly a pointless pattern of repetition with the next convenient Baddy Of The Week to harasses you. Nothing really happens, there is no overarching plot, or threat, because everything HAS to be tied up in a cute little bow just enough so the world will limp on long enough for the next character to get their shot in the revolving door of relevance. This "1 game 1 character" nonsense needs to stop. It is butchering so much potential. A character getting more than one game does not mean they usurp this entire Franchise.
Solas is clearly someone that was planned from Day 1 of Dragon Age Origins. There is evidence everywhere to support that line of thought. This is the first time this setting has actually had a bad guy that can be more than just Baddy Of The Week. But by continuing this pattern of Revolving Door heroes, they remove all emotional investment the characters have regarding the figure in question. The new characters don't have the emotional baggage that will make fighting them so worthwhile to begin with. Sure the players have it to some degree, but not as much as they would be if the character remained the same until that particular bit of baggage is stored away. Shepard is the best example of this. Replace Solas with Saren/The Reapers. would you have really been all that invested if Shepard ACTUALLY died in ME2, and got replaced by either Miranda or Jacob? Then they die or get crippled or w/e and another guy took over in ME3 to finish the fight? I highly doubt you would have been. Particular antagonists are linked to particular protagonists, due to actions over the course of the story. Simply slotting another guy in to deal with him diminishes the experience in ways I cannot express.
Solas is linked, irreparably to the Inquisitor due to their interactions. He played you, utterly and completely. You were a tool, not even a person to him. A bug who destroying is a mercy he wishes to grant you, because to him your life has no value or meaning. He tricked you into cleaning up the mess of his failed plan to destroy you and everyone you ever knew. You were nothing but a pawn on his chess board, all while possibly whispering sweet nothings into your ear and telling you how important you are to him. This is betrayal of the deepest levels. things that rock a person to their very core. Your character declared, in no uncertain terms, that they are coming for him, because of what he did. What he did not just to the world, or what he plans to do to it, but what he did to you. It is Revenge, it is Closure, it is Justice, it is Love, it is Rage. It is all of these things. The whole game was not about Corypheus, he was merely a side affect of the cause. The Inquisition was formed to close the Breach, to find and stop those responsible, and restore order to the chaos, with or without anyone's approval. That duty has not been fulfilled. The culprit is still out there, and has no plans to stop. This story is not over. The Warden's story IS over. Hawke's story IS over. THIS one though....is not over. It is in fact, just beginning. Because the gloves are off, no more masks, no more deceptions. Everyone knows who the players are now. Now....now the real battle begins.
They don't need to be the PC in the future, they just need to remain relevant. They need to take an active role in the events of the future. They need to be more than just "That one special guy down south who did stuff". They need to be, perhaps, a PC you take control of for special events, like the Joker sequence on the Normandy, or the Companions at Denerim's Gates. One of those special moments, has to be confronting Solas. Hell that can be the ONLY special moment for all I care. They can be an active cameo for the rest if they really refuse to budge on this. But they must, without questions or hesitation, be there at the Final Confrontation, and we, the player, need to have control over what is said. I cannot express any clearer why this HAS to be. I've never been more sure of anything in my life as someone who enjoys fiction or story telling. I was ready to put the Inquisitor aside, ready to move to on to the next guy out of the revolving door. But Trespasser has changed everything about this character, and their relationship with both Solas and this Setting as a whole.