It fun that this question comes today, last night I was saying to myself that all audiobooks from audible sounded the same. But AWS TTS quality is bad so the closest would be play.ht, 11labs and lately open source voice craft and open voice

https://huggingface.co/pyp1/VoiceCraft_830M_TTSEnhanced

https://research.myshell.ai/open-voice

The main issue is the time and sentiment.

It shouldn't take long before someone takes openvoice and start taking books and tts them on a platform.

The main issue will be legal to negotiate right with copyright owners this is where the game is... purely lawyers