That would truly force a very heteronormative view with core family values upon the player. My Tav is a woman, where did this baby come from? (I am not sure I even want to know!) And not everyone sees a Jane Austen fantasy as their dream relationship. Yes, Shadowheart expresses this as a future she would like, but I find her character to be very open minded and receptive to Tav's wishes as well. So I don't think she would force them into a certain lifestyle. I think it's best to leave certain things unknown so the player can paint their own picture of their future. Sure you could put a bunch of flags and checks that only leads to this ending under very specific conditions, but that seems like a lot of work and their track record with implementing flags and checks properly isn't exactly stellar.
I am not accusing you of any bigotry or anything, I don't think you meant it with any sort of malice. It just shows how these norms are so prevalent and can unintentionally exclude minorities and other people.
It's an interesting thought, because there's still the matter of the (bugged, imo) dialogue options that update which are only available once eventually updating to her essentially asking you to "get her in a family way". And since it takes an entire playthrough of not asking her the question (that's available the second you meet her on the beach) before you have it updated to that, nobody seems to know if this dialogue changes based on Tav's gender.
Because if it doesn't, then the game seems to follow the 5e rule that lesbians can have children (according to Backinstyle, but I believe him her (5 hour late edit, misgendered, sorry!)! I'm no expert on the matter). Which is actually relevant for Karlach and Lae'zel too (I know Lae'zel can't bear children, but I don't recall if that was a permanent thing, and besides, Tav still can unless you roleplay one that can't).
Edit: There is the matter of a Gondian lesbian couple that has a child as well, but it's not explained if that was through adoption or not, since it's not really a big talking point while they're being oppressed.
