The Warden didn't have a voice back in DA:O. If BioWare brings them back, they'd be forced to give him/her a voice, and believe me when I say that a lot of people WON'T like that. And if they bring them back, many people would complain about how he/she is not the character they played in Origins
Revan was a non-voiced cypher for the players to inhabit in KOTOR.
As for the very likely differences that will appear between the portrayal of the HoF and the players' headcanon, well, nine years stand between Witch Hunt an Inquisition's beginning: people change in a decade.
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The Warden if still alive is seeking a cure to the Calling. [...] They are alive and well and their story ended in DAO
Indeed, but by allowing the possibility of the Warden surviving the fifth Blight and rising through the ranks to become Warden-Commender in Ferelden, the writers dug a hole they can't get out of:
The Warden's tale was complete at the end of Origin, that's absolutely true. Even Awakening isn't really the tale of "The" Warden: it's the Tale of the Commander of the Grey in Ferelden, who may be the HoF but whose origin is virtually inconsequential in this story.
The problem is that the writers keep bringing back the story into the Warden's home turf. A surviving HoF being invisible in DA2 wasn't a problem at all: s/he was busy ruling over an Arling located on the other side of the sea. But Inquisition put nearly half of the action in Ferelden, a large part of the plot involve the Wardens being enthralled by Corypheus because the Orlesian commander of the Grey panicked while her Fereldan counterpart was absent, and now they bring in more Darkspawn and potentially the Architect as well.
The Warden's story is over, yet Bioware's writers, despite being openly unenthusiastic about bringing back Origins' protagonist into the spotlight, keep making new stories involving his/her legacy, and predictably, people seeing keep asking for the Warden to reappear onscreen.
Which is why I maintain that the best thing to do is to bring back the Warden... in order to give him/her a definitive unambiguous plotline death and be done for good with this character.