No one ever said that he should play a significant role, only that he plays a role.
Having him be the King of Ferelden doesn't mean he has a significant role in the series.
I agree that it doesn't mean that he has to play a significant role. I was responding to comments like these:
I agree that I doubt that's what Morrigan has planned anyway, but it might be an interesting plot point in DA4:Rise of the God Child
So, yeah, people are claiming that he will play a significant role at some point. There have been about two dozen posts like this over the past week.
I don't understand why people keep saying this given Alistair can take the throne on his own without marrying Anora, and his father never recognized him. In cases where there's no legitimate heir, an illigitimate one will do.
Yes, but it doesn't make him "a prince". Again, just being the son of a king doesn't make you a prince. You can inherit or seize a throne without being a legitimate heir. This kid, if he even exists, isn't a prince, regardless of who his father is.