Currently you can co-author with chatGPT and get a book of arbitrary length with enough revising, re-generations, and trial and error. The book will be ok, albeit cliche-ridden and surface level in a lot of areas but it'd be readable and worse books would certainly exist. Will we ever get to the point that we can do it with the click of a button? Probably. But that alone is super human. If you were told to write a book about a topic it would take you a lot of revising, rewriting, and trial/error too.