It appears that audiobooks are coming to the Play Store at some point in the future. Strings of code found in the latest version of the Play Store APK reveal that Google plans to integrate audiobooks as an option to into the Play Books section of the app, though not necessarily in its own category and may simply present them as an alternative option to standard ebooks when looking at a specific book. Currently, audiobooks aren't available on Google Play and there's no indication of when Google plans to introduce them, but they are apparently on the way.
In addition to audiobooks being available at some point, the Play Store is also getting ready to showcase notifications for apps and games that people have installed on their devices. What the notifications will actually be is unclear, but it looks like Google plans to install a new button in the Play Store which will hold a counter to alert users to how many notifications are unread, and tapping on this button will presumably break notifications down on an individual basis for the installed apps and games. The notifications could be anything from changelogs to notes from the developers or publishers but there's no detail as of yet what sort of information will be listed.
The Play Store will also start offering a deal of the day at some point. There's not a lot of detail about this particular upcoming change, but it's likely that each day Google will be offering a deal on a new app, game, book, movie, TV show, or song which users will be able to take advantage of. Google lists deals on all the content in the Play Store all of the time, but it looks like there will now be a designated section and listing for what it considers to be the very best deal that users should check out. If you're someone who dislikes that the auto-update feature of the Play Store doesn't allow you any control, that might be changing soon. The Play Store seems to be getting an option that will allow users to designate that auto-updates are for system apps only, whereas third-party apps would be updated manually by the user instead. Alongside all of these new things that Google is adding in, Google is seemingly taking one thing away, and that's the option to wait for Wi-Fi with app updates or installs. As it currently stands when you download an app or an app update, if it sits at a significant size, Google will give you the option to wait till you're connected to Wi-Fi before the download starts, but it looks like Google will be removing this down the road.