Some people will learn to use these AIs to make top-quality audiobooks (and books, movies, TV shows, comics...). It will be a more manual process than pressing a button, but still orders of magnitude less than what it took before. As a result there will be a tsunami or high-quality content.

There will be curation and specialization. Previously ignored niches now will be economically profitable. It will be a Renaissance of creativity, and millions of jobs will be created.