But for real, I think if Karin was to be Sarada's mother, there would be a lot of dangerous dramas that would make the story more mysterious and cool (Uzumaki lineage, Orochimaru's hideouts, more contact with Mitsuki, mysteries of Konoha etc)
That's quite strange, specially after Karin mentioned she became "friends" with Sakura, helping her give birth, gave glasses to Sarada etc. What do you think that happened?