I know AI art is a thing. Will there be worry of AI authors?
I'm calling this "unlikely". We may, in fact, now be at roughly the peak performance of generative AI, for technical reasons. If it cannot write a coherent story now, it is unlikely to do so affordably.
Why? Because generative AI is basically a statistical model. Improving its performance requires increasing the amount of data you feed it. Broadly speaking, for such models, to reduce the errors by half, you must quadruple the amount of data you feed the thing.
The problem is then that the models have already been fed most of the readily available data that can be scraped off the internet affordably. There isn't enough English-language prose lying around to double, much less quadruple, the size of training sets.
Further improvements are apt to call for actually paying for content, or paying very smart humans to accompany the AI with complicated sets of heuristics. Either way, the cost of the AI skyrockets. When the major point was that AI was going to be cheap, that's a limiting factor on the AI.