I have been a great fan and listener of Audible since 2015. I am currently busy with my 44th title. If you are not a customer, the way it works is, you sign up for the service and you pay a certain amount for credits. I am on the plan where you get 1 credit a month. 1 credit can then get you any audiobook you like, whether it is 1 hr long or 100 hours. You can of course purchase more credits if you would like to listen to more than your one book per month. I tend to buy books in the region of 15-40 hours, so typically, I am a credit or two behind since, I will not likely finish a book in a month if it is a long one 30-40 hours or so.

I do however, wonder how an audiobook subscription fee, in the Netflix, all-you-can-listen style would fare?

I would care less about listening time, and would likely start to widen the variety of books I listen to. For example, there are often books in the history/non-fiction/business type categories that I am interested in listening to, but since they tend to be quite short, I avoid them since then I would soon be out of credit. A system like that would also be more attuned to giving up on books you were not particularly enjoying.

With Apple's big push into services, it seems like an audiobook subscription service might be a way for them to differentiate their books offering from what Amazon offers.