I always thought of visual novels as a niche kind of games. As opposed to other games. They are the only type of PC that could be played the same way without hassle on tablets, as they don't requires much controls or buttons, so they have a good chance there.
In recent years, they have been gaining traction with people, but I don't think they will become mainstream. They require too much reading, and while you get rewarded for that with a good story, it's not something many people would want to do.
As someone who wants to become a developer for these games (made short skits so far). I feel like they would be a bit harder to market compared to regular games, but I could be wrong here.