The help page for Google Play has recently included empty sections for "Audio Books" and "Magazines and Journals," which leads to speculation that these items might be added to the Google Play Store soon.
Google Play basically combines the present content offerings of Android Market, Google Books and Google Music, and puts all of it under a single banner. The upgrade occurs automatically, with Google stating, “if your device can be updated, the Android Market app will automatically update to the Google Play Store app." An addition of audiobook downloads and magazine subscription support would be a good thing for Google Play, to become a more complete competitor of Apple's iTunes.
Google also recently secured the unregistered domain names googleplaymagazines.com, googleplaynewspapers.com, googleplaynewsstand.com, googleplaytv.com, along with other variations, further suggestions their plans for Google Play.
Android users can obviously get audiobooks from places like Audible, and magazines can be had through Zinio, but Google Play seeks to streamline all of the present content available on all of Google's services to date.