Both of these, please!
If we're in Tevinter for DA4, I fully expect Maevaris to be a companion. She is too awesome of a character to be confined to a comic one-off. I've seen people even suggest Calpernia as a potential companion in DA4, and that could prove interesting. She was certainly a "shades of grey" type of villain. She had a noble goal but was willing to do horrific things to get there. Choosing to fight her lack of ethics or go along with it could be a fun RP opportunity. There isn't a scenario in DA:I in which you can definitively say that she's dead so she could certainly come back in some fashion.
And again, adding to the idea of going to Tevinter... I would expect to see Dorian and Fenris return. Possible recurring companions? If so, I'd prefer one or the other. I like both characters but am enjoying the DA method of giving us a new batch of companions in each game. I didn't mind seeing Varric again, so apparently I can tolerate one.
Maybe Scout Harding? Assuming she isn't followed up too much in DA:I DLC. She could be scouting someplace north for the Inquisition (maybe spying on the situation with the Qun for the Inquisitor?) and gets recruited by our protagonist from there. She could have a lot of different dialogue depending on how we played DA:I and give us updates on what our Inquisitor is up to.
This. This! So much this! I love the idea of Dorian, Fenris and Scout Harding coming back as important characters and introduce Maevaris into the game as well! I especially hope Maevaris is a companion and Dorian takes the role of an adviser (or something similar) akin to that of Leliana. I also hope that we see more of his relationship with his father and struggling with the issue of trying to change Tevinter society. I also hope Fenris returns either as another adviser or as the leader of a much more organised and dangerous slave rebellion that's a main part of the story (if he was killed or with a romanced Hawke, maybe another character can take his place). As for Scout Harding - companion and love interest please!
And, yeah... Zevran got shafted, but Leliana went on to have a couple cameos in DA2 and then had a HUGE role in Inquisition.
Every now and then someone says something similar about Sera or Blackwall or Josephine (compared to, say... Solas or Cassandra. He's apparently a god and she's responsible for dragging you to the Inquisiton in the first place, and she can also become Divine).
So, assuming any of these characters pop back up again in future installments, which less plot-central character could potentially be given a bigger role in the plot than they have now?
I have no doubt that Sera and Solas will turn up at some point in the future. I have a feeling Solas will at least have a cameo in DA4 and have a bigger role in DA5 and/or DA6 (assuming Bioware ever gets that far). As for Sera,
then she'll definitely have a big part to play in the future. As for Zevran - here's to hoping he gets an important cameo in a Inquisition DLC or something. Still at least he got (a very buggy) one in DA2.