this is a specific niche
Hmm. While only 1 in 4 of the vn here is adult, about 2/5 of the adult games here are vn. 1/8 of the vn are horror, but vn tend to go for the psycho horror. Prime offender is doki doki literature club. Only about 1/100 are tagged gore, but that tag is not popular to begin with. Some people do not even know what it means or use horror instead.
I do not like linear or kinetic visual novels very much. Too much like reading a book or watching a movie. Nothing wrong with that, but if I play a game, I want to play a game, not play as in play a movie.
Gore or naughtiness does not really add much to a story. It is a setting or style. It has to fit the rest of the game to add to the story and you can easily overdo it or botch it and appear cheap or distract from the story.
But basically, every "nieche" has it's audience. Violence and romances are just prime motivators for any kind of plot, so they are used so often and in so many variations. A visual novel about stamp collecting might be doable, but unless you make a pokemon collector game variant out of it, I do not think it's audience will be very big.