There's some contemporary discussion of what happened here: https://tidbits.com/2009/03/02/why-the-kindle-2-should-speak...
I think there is still integration with Audible, though. If you buy a book on the Kindle and on Audible, the position will sync, and you can switch between listening and reading without losing your place in the book.
I tried it while on a treadmill so it allowed me to follow the book with more focus without sacrificing much else.
It wasn't a good experience but it was nice to be able to keep 'reading' a book while I was exercising.
It worked for me for over a decade, until I broke the device. I don't know if I never updated the firmware or if the fact I used Calibre to convert books bypassed the feature gate.
It's more of an open problem how to create those epubs. I have some code that can do it using Elevenlabs audio, but I imagine it way harder to have something similar for a human narrator.... who's going to do the sync? Maybe we need a sync AI.
For Android:
- Moon+ reader pro - some paid high-quality TTS voices (like Acapella)
For iOS:
- Kybook reader and internal iOS voices (no external TTS voices for the walled garden)
This works well enough to listen to a book while you walk and when you get back home read on the WC from the place you stopped.
Additionally if you buy a tablet or an android ebook reader, you install the app there an you can continue on your bigger/better device seamlessly.
Whisper-sync for the masses! Ahoy...
What surprised me a good way was my Kindle app was aware of this and asked if I wanted to download the audible version of the current book I am reading.
Been listening on the way to work and then reading on the way back. Enjoying it so far.
Not quite seamless but it works. It has a cursor that follows the words as they’re spoken to, which allows you to read and hear (“immersive reading”) which I find to be extremely helpful for maintaining focus.