Each Dragon Age has it's own unique protagonist, the Warden can only work as a silent protagonist because that is how they were designed. They can't work as a camo.
If anyone wanted the Warden back as a camo. thought about it for more than a few minutes, they'd realise what a bad idea it is.
- The Warden never had a voice and since all DA NPCs have always been voiced, BioWare would have to pick a voice for you. Now image that, BioWare choosing what voice suits your Warden, it would never be like how it was in your head. Everyone would freak out.
- Unlike Hawke, the Warden doesn't have a 'personality' that BioWare can use to create their dialogue from. Everyone word that was uttered by your Warden could be totally out of character for your Warden because BioWare has no guide to create their responses.
- Unlike Hawke, it was possible for the Warden to be dead after DA:O, so they are risking the hatred of their fanbase for a camo that won't exist in a lot of World States.
The Warden's camo was suck for anyone who wanted it.
The Warden can only work as a silent protagonist of a new DA Game, which quite frankly I can't see happening because BioWare has always said that DA is about the story of Thedas not one particular person in Thedas.
It can't work as a cameo because you say so? No, you'll need an actual reason, if these are yours below, well here you go, it took me 2 minutes.
1) You'd pick the voice type, as you do with your character.
2) The title, and plot surrounding the warden, all the experiences you put him through and shaped are his personality. - This is not hard to cater to when written well. His/Her personality is already shaped, it doesn't need to be re-shaped or explained further hence why it is a wasted opportunity not to put them in, or draw on it.
3) They pulled this off easily in awakening, and indeed every other time a character has been dead, in every other quest or story.
4) The warden could work as a silent protagonist quite easily actually, if the cameo was action based and he or she were assisting you in a battle or some such. You could have a quest to discover what happened to him/her. You could have someone silently turn up, pick you out of rubble save your backside and be on his/her way. The entire mission or quest could FORCE him/her to be silent. You could have a diary from the warden, letters from the warden, clues from the warden, magical dream sequences, visions, anything.
We weren't asking for much just some fanservice, could be done in the matter of few days with access to the right tools.
I believe the saying is "Don't fix what isn't broken"
Why on earth does anything need to be altered or fixed? There are a hundred ways to write this that wouldn't change a thing about the character.