Well, there was that concept art, where Cullen is wearing a simple brigandine instead of his fancy lion armor. Maybe he starts in that simple outfit, but then something happens, and he gets a fancy outfit as a reward for a quest. Because let me be honest, that armor is so not him. He's a simple Fereldan guy from nowhere, who's made himself out of nothing, and that lion armor looks like something a chevalier would wear, or at least a nobleman with more money than he knows what to do with. Maybe some dying chevalier gives it to Cullen at some point for some chevalier-y reasons, like honor and glory.
Totally agree that it's not him. I'm just praying that the hide helmet toggle also applies to specialists. 
On the concept art... TBH, my guess is that the boring blue surcoat on him and, arguably, on Leliana in the War Room concept were placeholders of some kind. Even in the leaked survey concept art from 2012 he was wearing this same new furry armor, minus lion, so my guess is that that's his iconic look for DA:I. (heh, minus sword of mercy, of course
)

He's also wearing it at the moment the Inquisitor declares "we are the Inquisition" which ostensibly happens very early in the game (altho, this just as easily could be staged for the trailers).