[fjtorres]

I'm getting flashbacks to the 2010/11 reports that some ebooks were outselling their hardcover edition. A couple years later, ebooks outsold hardcovers at Amazon and shortly afterwards, paperbacks (though that was mostly through the decline of the massmarket paperback). Today there are several genres where ebooks make up over half of unit sales. (And others where they barely register.)

When I sampled Audible, the category where audio really clicked with me was non-fiction.
I can easily see a good portion of non-fiction (self-help, biographies, histories) going strongly to audio.