Approaches based on tagging and interpreting metadata are tempting. Building structured human knowledge into the system seems like a good idea. But ultimately it isn't scalable or effective compared to general learning from large amounts of data. It's exactly the famous Bitter Lesson. http://www.incompleteideas.net/IncIdeas/BitterLesson.html
To the extent that authors provide supplemental notes or instructions to human actors reading their books, that information would be helpful to provide to an automated audiobook reading model. But there is no reason for it to be in a different form than a human actor would get. Additional structure or detail would be neither necessary nor helpful.
The difference is production moves from multiple people / skills to potentially one person, the writer, who ideally already knows emotions in scene. Economics makes sense before one click audio book / production as long as it's subtantially labour reducing.
To the extent that authors provide supplemental notes or instructions to human actors reading their books, that information would be helpful to provide to an automated audiobook reading model. But there is no reason for it to be in a different form than a human actor would get. Additional structure or detail would be neither necessary nor helpful.