I think the reason why so many of us are attached to the Warden is precisely the reason BioWare could not bring him/her back.
As a voiceless protagonist with no set tone and no auto-dialogue, the Warden is a blank slate. There are in effect 6 Hawkes and 6 Shepherds to manage (human male/female x diplomatic, humorous, assertive). There are thousands of Wardens. Between the origins, the non-transferable specializations and more importantly the personal role-playing each one of us did with their Warden, the personality we individually projected into that blank slate, bringing him/her back as a playable character would be one giant booby-trap waiting to explode in BioWare's face. We as players gave the Warden personality - not BioWare per se. As such, I can't see how there is any "one size fits all" way to bring him/her back in a way that would satisfy the fans.
I mean, people complain that Hawke in DAI looks nothing like Hawke in DA2 despite the fact it's a brand new engine. And that's just superficial. Can you imagine the outrage if BioWare "messed" with the Warden in a way that doesn't fit with someone's headcannon?
I love my Wardens, I really do. But as a playable character, BioWare gave me a lot of time with them, between DAO, the expansion and the DLC. I can let it go. I would definitely prefer knowing what happened to him/her and him/her not be forgotten, but I don't need to be in direct control anymore.