I think it'll always be "human decides what book is about, cues AI, then gives feedback to AI to refine output," The cues will just need to be less specific and well crafted, and the amount of feedback required will go down. Maybe eventually AI will be able to one-shot amazing novels, but they'll still need taste makers to read the output and promote it, which isn't really much faster than a taste maker asking for what they want directly then reading/requesting changes.
