Interesting question hat I hadn't actually thought about before.
However:
a )there's a strong implication in the game that warden's are either infertile or 'almost' infertile so a child is unlikely even if Anora was not infertile
b)Maric Theirin got his surname from his mother so I'd assume that a potential Cousland/Mac Tir child would also take the name of the mother/queen rather than that of the prince-consort.
c) the OGB with Cousland as the father is completely unimportant for Ferelden's politics no matter which way you look at it. Even if Morrigan was willing to let it go, it was raised in court, the dark magic origin of the child remains secret and it's not a mage...
d)The only way it could be important was if Alistair was the father and Anora had no children. And even then it remains questionable that it's claim to the throne would be supported as again it would need to be raised at court,not be a mage and the way it was conceived would need to remain secret