Berserker would be cool, especially since Dwarf Warrior is a playable thing again. Maybe the Berserker's first power could be a passive that lets the warrior dual wield 1h non-dagger weapons, and allows them to build guard on basic attacks, and they could have special attacks and utilities that spend guard. Just a quick design theory I thought of just now.
The absence of the duelist spec was kinda disappointing. In DA2 you could tank the game with duelist Hawke or Isabela, and it was a lot of fun, so I was personally kinda sad to see that option was no longer available. Though I could see why they might've decided to remove it, since that playstyle offers a lot to dagger fighters and practically nothing to a bow rogue (Bow tank? /nope). Since you're locked into your spec in this game it would be kind of horrible to go duelist as an archer and find nothing that supports your playstyle. And trying to design a spec that could let a dagger rogue tank and still offer something viable to archers would be rather difficult. I hope they can eventually do it though because dagger tanks are awesome.
I can also understand why they didn't do Blood Magic since a number of important main characters in DA:I would probably freak out if you became a blood mage. But I'd still love to see it return as an option, somehow.