Audio has been around since, I suppose, the spoken language. The difference now is distribution and availability. Audiobooks, podcasts, smart phones, voice controlled home speaker systems, connected cars, and who knows what will come next.
The ultimate in content repurposing.
This is where things can get exciting with your book as a podcast as opposed to (or in addition to) an audiobook.
I want to write my own stuff, and, you know, it would be nice to put myself in it. But I would like to...