Enshittification isn't adding new features that people want, it's gradually lowering the quality of the product. So here if Audible is solely adding more possibilities, never at the cost of higher quality ones degrading, then indeed I'm wrong.

If though they hire less people to do good voice acting, then it's really shitty.

I genuinely hope I'm wrong and they are ONLY adding new capabilities... but my entire experience with capitalism is that obtaining a monopolistic position is not done to improve quality but rather to increase margins regardless of how.

We'll see!