In DAO, I would've liked another Rogue and another Mage in particular, which I had planned on if I could add a few things to the game. There was a hope of possibly adding a Dalish Elf with the Ranger ability from the clan if you helped them by either killing Witherfang or reversing the curse. The Mage, kinda obviously, was recruiting Jowan. Both of them would have been inducted into the order at the end of the Landsmeet quest. Lanaya would've been fun, but I like her better as leader of the Dalish Clan. (Hope we see her again!) If Daveth could've survived, he would've been a fun companion! Another idea was giving a story to the Chasind Doomsayer in Lothering just to give a different perspective on Ferelden and the Chasind.
In DAA, Mhari was the big one. I wish she survived her Joining and a different person died. Beyond that, having a Disciple join you could've been an interesting twist.
In DA2, I wish you could've saved the twin sibling who dies as you escape Lothering. Having the three Hawke siblings stand together in a party could've been a lot of fun, especially in terms of banter. Beyond that, having an option to recruit Ketojan would've been epic!
In DAI, Scout would be fun, but I like her role as is and only wanted a full love story option over the tantalizing flirting they give us. Sigrid would've been an interesting view of Avvar life. Maybe being able to recruit a rebel mage would've been fun, though I can't think of one in particular, if only for the banter between the new mage and a certain Orlesian mage companion.