While I want to believe that Solas is Fen'Harel and Solas is just the totally-not-subtle name of self-loathing he takes after awakening and trying to fix his mess... there IS something odd about his interactions with Cole.
When Cole begins interacting with Solas, Solas goes out of his way to ask Cole to remember the things that pain him or weigh on his mind, "could you.. could you do it as I would?" In doing so, Cole changes his syntax and sentence structure. It's no longer a disjointed garble of verbs, but instead complete sentences that have a subject. Him. In third person. No longer the first person in-the-moment-experiences he has with the other companions.
This separation, or personal distance if you will, could lead credence to the concept of Fen'Harel possessing Solas at some point. Who knows? That possession could have even been before the fall of Arlathan and Solas could still be the ancient Elvhen Abelas recognizes him to be.
Moreover, in Cole's descriptions of Solas' past there is a moment in which he describes a death scene:
Cole: It sees him ready to jump pain pulsing. A life of frustration can finally fall, to freeze.
Solas: Ah, yes.
Cole: It holds him high, shows the hole where everything falls without him. He never needs to leave. He matters here.
Solas: That is one interpretation, yes.
Cole: You think it is different?
Solas: I think he fell and it held him as he died. Leaving him with images that told him his life was worth while.
Cole: That's much sadder, but yes, calm comfort as the cold takes him away. They can only return to the maker if they become real. Why can't they be forgiven as they are?
Solas: People say the lack the ability to learn or grow.
Cole: Yes?
Solas: But the more contact you have with this world the more ability you gain.
Fascinating. Why would Solas have the memory of a dead man, the sensation and thoughts he felt as he died? Moreover, their conversation flits straight to a conversation about being "real" (seriously, that's going to be my next wall of text break down - that word bothers me to no end because of its ambiguity), the necessity of becoming or interacting with the physical in order to grow, to change, to experience. It's odd.