I think no matter what way you look at it, implementing the Hero of Ferelden would be near impossible. Since they have no voice actor, and the options for their dialogue are very broad, there's no way to have them be properly our Warden unless we're the ones controlling them (Can I get a play as My!Warden hunting for cure DLC, though?) . If they can't do it right, then they shouldn't do it at all because all it would result in is lots of angry people upset that their 'canon' had been stomped on.
Don't get me wrong, I'd love to play as her again, but honestly in Inquisition even the vague letter was very unlike 'my' warden and I would've been happy without it. (Still grateful, of course.) 
Hawke was different because she had one of three personalities depending on the things you chose. She's her own character in her own right, much like the Inquisitor, or Shepard.