Sam's reveal has clarified it for me--he's the only human we've seen without a soul
What about Aaron, who we saw in the episode where we met Balthazar? Wasn't he missing his soul until Balthazar was forced to return it?
I wonder now if Sam will come together with absolutely no memory of Hell, since his "conciousness" was never there
I'm not sure what to hope for, from a storytelling perspective. Because at the moment the "happy ending" we're looking forward to, the return of Sam's soul to the empty shell currently travelling about with Dean, would seem to promise a whole boatload of traumatized/freaked-out/climbing up the walls and across the ceiling Sammy. That's if indeed he's awake and aware of what's going on while he's locked in with Lucifer and Michael. It wouid make for an interesting fanfic, but I think it would be a pretty grim set of episodes watching Sam fight his way through something like that. (Or maybe not, considering Show doesn't tend to linger over aftereffects very often.)
Dean came back with his memories intact, and he came back with angelic intervention. If Sam comes back without the aid of benign powers I wouldn't think whoever is helping him would be interested in cushioning his psyche by helping him forget.