This is true - we've taken advantage of it somewhat (my wife ripped Harry Potter this way, and we recorded ourselves narrating some favorites).

Mainly (shamefully) "Simply remove the DRM" is doing some work in your sentence. We just, uh, haven't gotten together the executive function to figure out how to do it with the Libby app on the iPhone. As a Hacker News poster I want to be the type of person who figures this out. But, I have not.

That's fair, library systems can be very variable, where we are we can access audiobooks on a desktop, so there's access to the raw files, I can see how if you're doing it with an iPhone app it's considerably harder!