I don't think that's true. SOTA open source is still much worse than eleven labs and requires a dedicated modern GPU for any kind of speed of generation. Certainly can't on-demand, on-device on an iPhone.

Apple already is doing very high quality generated audiobooks, but you do it for your book as the author.

https://authors.apple.com/support/4519-digital-narration-aud...

"Mitchell" sounds exactly like a very popular narrator "Ray Porter".