I love audiobooks on Spotify. Unfortunately, they are currently accessed in very similar ways to regular music. They are organized in albums, there is an option to shuffle and there is no way of knowing where you stopped when you want to come back to a book.
Podcasts on the other hand, show you which episodes you've already listened to and the buttons Shuffle and Repeat have been replaced by "Skip 15 seconds". Those features would be great for audiobooks.
The change should be fairly easy to implement, since all the features are already in Spotify.