I guess I kind of wish they would just offer the AI narration as a feature of Apple ebooks. Such that, if you buy the book, you can have ebooks read to you by your phone. I am really just buying books off audible with the subscription they offer. There are some books (tech books that is) that are offered as audio books and I gobble those up. There are, however, many more epub/digital books that I never buy not because I'm uninterested in the content but only because I don't have the time to sit down. I assume that for said books the audience isn't large enough (and may never be) to merit anyone ever recording the audiobook.
There are certain books that I think I'll always buy the non-AI variant because narrators can bring more than natural reading, they sometimes bring different characters (sometimes more feminine, more baritone, more stereotypical accents) -- and I would melt if AI could do that kind of voice acting.