May I ask why that matters? I'm quite happy with this question remaining in limbo, since personally I prefer to not have a relationship sanctioned by an organization whose legitimacy to regulate such affairs I question. The relationship between my main Warden and Morrigan does not need to be sanctioned by anyone or anything.
It matters in as much as I wouldn't mind knowing what the official stance is, but if that's not not happening then I'm fine with headcanons. I tend to agree that neither Morrigan nor my warden would really care about what the chantry has to say about their relationship.
She talks about his destiny, all that she has worked for will be for naught, he is more than that, etc. After Mythal took Urthemiel's soul from Kieran, Morrigan was like :- "Kieran had a destiny and now Flemeth took it away, etc."
I am not saying she does not care for Kieran. If you do the Dark Ritual, she cares for Kieran as a boy with an Old God soul first followed by Kieran as her son.
If you do not do the Dark Ritual, she cars for Kieran as her actual son first and foremost. She treats him as a human being who has choices in life, not one with a destiny she determined for him.
It does bug me a bit that we get to see Morrigan talk more about Kieran if he's a regular human, but I think that is less about the character and more about content. Human Kieran doesn't get the scene in the fade, so anyone that didn't do the DR but still romanced Morrigan would get less content, hence why human Kieran gets more dialogue options from Morrigan.
I do agree a bit that Morrigan's initial attitude towards Kieran will vary depending on if he's the OGB or a human. But the scene in the fade really shows that by the end of that storyline Morrigan has fully embraced the attitude she has towards her human son as the one that she has towards her formerly OGB son. And I'd say that offering to sacrifice her life for Kieran's sake has nothing to do with the OG soul. That's the action of a mother trying to protect her child.
Basically, in my mind, what it comes down to is when exactly Morrigan realizes how much she cares about her son. I imagine the surprise pregnancy with the Warden's human child has her going through a gamut of emotions ending with her realizing she loves her son earlier on, while with the OGB version she's more likely caught off guard by her emotions for the child, but she has the excuse of "It's all part of the plan" to hide behind so she doesn't have to admit that she cares about her child more than the old god soul.
The line where she's lamenting the loss of Kieran's destiny, it came across to me less like "Oh woe is me I lost the old god soul" and more like she believed that destiny to be a good thing for her child.
Also, head canon time: The knife that Morrigan uses to kill Abelas is the Warden's old killing knife.