I'm wondering if this statement by Sera has anything to do with the Transformation part. "You see Sam in a state he’s never been in before pretty much at the top of the episode, she says. Structurally, he does a couple of pretty interesting things in that episode.”

Structurally? Could be construed as a transformation I suppose.

I'm hoping Castiel will become an archangel personally...he certainly deserves it after all he's been through with the brothers, even if he has done some pretty bad stuff to get the war in Heaven won.