I can speak to this somewhat but first I would have to absolutely agree with you that overall there is little to no understanding or acceptance of this. As a therapist I can not recall ANY of my education or training even mentioning such a thing, but when I first called my advisor soon after BD looking for some kind of direction she seemed to have an understanding of what was going on. No labels applied to it, but she did tell me things that did not make sense to me at all at the time but are now crystal clear. One thing in particular is that my W was not my W now and that I should not expect her to act as the same person. She also strongly encouraged me to pray daily and to do what I would be able to look back on 5 years from now and be proud that I did. She used the term "fighting for my marriage" which really meant standing.
My parish priest seemed to grasp what was going on and applied a spiritual component to it. He was the first to use the term "shadow side" and was able to expand on what my W's motivations were (finding her identity, seeking to find value in her life etc). He had seen and/ or heard of such things before and said at the time that this could go on for years. He asked me if I would be willing to take her back and said that she would have to pay some type of penance for what she had done. This was an alien concept to me at the time as I just wanted her to come home one way or another. His point was that for me to trust and forgive her that she should pay a penance, and even told me that I would have grounds for seeking an annulment if I so chose due to her issues stemming from before we were married. It was alot to think about and I have pondered the words of both over the past year. I've been planning on contacting them again and this thread just reminded me of that....
One day at a time.
Thundarr