CapnZapp
Legend
I think a game set in a vaguely Witcherversy setting would be fine, and it should be "as European as possible".This is whhy I disagree with @Laurefindel 's proposal to keep it as European as possible.
Not every game should contain every option.
The question should instead be: should THIS game be that game?
And here I agree with you. Since Birthright is a D&D game, a WotC game, a Hasbro game, it makes sense for it to be an everything including the kitchen sink setting.
So I would expect it to be reimagined to include MORE real-life cultural "inspirations", not less.
The old Cerilia was pretty much following the Mediterranean-centric (is that even a word?) approach, with Vikings and Old Araby as thhe furthest extents of what's considered "exotic".
This would very likely be extended to cover the entire Earth in a new edition.
As I said, the actual specifics of the Cerilia map was always the weak generic part of the Birthright concept. Nothing is gained by clinging to the old map.
It is the IDEAS of bloodlines, awnshegn, and domain overlay that makes Birthright valuable.
Now that I think of it, maybe Birthright would work best as an optional plug-in for each of Hasbro's existing D&D campaign world...
And not be its own thing at all, I mean.