This kind of fanfiction could potentially explore Hermione's curiosity or it might be used to develop a complex plot around her character's exploration of different aspects of sexuality. But it really depends on the specific story and the author's imagination.
The first appearance of lesbian porn stories online is difficult to determine precisely. It likely occurred gradually as the internet grew and different types of content became available, without a clear-cut beginning.
Yes, in a way. They are mainly targeted at lesbian or queer - identifying women who may be interested in reading stories that reflect their experiences and desires in an erotic context.
Definitely not. These stories can cover a wide range of topics. They could be about the girl's journey of acceptance, not just of the relationship but also of herself. It might also be about the exploration of new social circles or lifestyles that the lesbian character represents, rather than just a focus on a romantic or sexual relationship.
No. While sex is part of it, there are often other elements. There can be elements of character development, like how the dom and sub characters grow in their relationship. It can also be about exploring different aspects of one's personality. For example, a submissive character might discover new strengths through the relationship.
The main distinction of porn with a story genre from regular porn is the presence of a coherent narrative. Regular porn often jumps straight to the sexual action, while the story genre tries to add some kind of story framework around it. But in the end, both are adult-oriented and feature explicit sexual content.