Solas: Not as a companion... But we NEED answers.
Flemeth: She was creepier than ever in DAI and I want her more than Solas. Lets have a doppelganger show up. How does that work, eh? She gets "released" in Kirkwall even if you don't kill her in DAO, right? Then there are two of her. That'd explain why Witches of the Wild got all the way up in Antiva or whatever.
Iron Bull: Not as a companion, but if we're in Qunari/Tevinter Lands it'd be nice to see him.
Dorian: He didn't really do much to redeem Tevinter, did he? Sure he helped us out, but public opinion of Tevinter only got worse in the end I imagine.
Isabela: I want her BACK. She was hilarious. And I think it'd be interesting to have a romance option from an old game again, it'd make more sense for her than for someone monogamous like Leliana, who wasn't an option due to that.
Maeveris Tilani: I haven't read the books, but I think that'd be so cool to have her in the game. It'd make sense for Tevinter, and she has a cool name.
Sten: Qunari.
So many more I could think of... You can really run with that Tevinter/Qunari Lands idea.