Seeing that picture of Fenris, I kind of want him to show up again... as a slave under Danarius because fuck Fenris. Even after all these years, I still don't feel bad for him. That guy couldn't stop whining and whining about mages in DAII. His character might have been a bit different if I played as Mage!Hawke, but he could not stop annoying me.
As for other characters I want to see, and perhaps the realistic options as well, Morrigan should almost be a certainty for DA4. If I recall correctly, she simply left at the end of Inquisition, and she had beef with Solas during the Well of Sorrows quest. I don't expect to see Leliana or Alastair again, especially considering those two have wildly different character states, with Leliana maybe being the Divine or not, while Alastair could be king, dead or a drunk. Also don't expect to see Cullen or Josephine again. As for the other characters from Inquisition, Dorian should be a safe-bet, while the rest seems done, from a character point-of-view.
I sincerely hope Bioware decides to go a bit smaller scale, in terms of world design. I don't need 9 different hub-world (especially not 3 different sand locations), and they should honestly just look to Trespasser for how it's done. I'm definitely in the minority in this, but something like Kirkwall from DAII, would also work very well for me. It's silly to get hyped so soon because I have such mixed feelings for this franchise, but I'm excited to see how they will finish Solas' story.