The first change is that Play Store listings will begin to feature additional information about apps so that we can "make better install decisions". It's unclear what that information will be, but it's likely to revolve around privacy and app permissions. And there's a new feature that'll enable you to monitor app install progress across all your devices, not just your current one.
These features appear to be server-side, ie. they run on Google's servers rather than locally on your device, so it's just a matter of waiting for Google to flick the switch and turn them on.
More new features in the Android September update
The Play Protect feature, which gives you security information about apps, is moving into the Security and Privacy page in your Settings app, and Google has already switched on improvements to the Play Store on Wear OS. Menu navigation has been improved for large screens in landscape mode, and you can hide recommended apps during the Google Kids Space setup routine. You can also install Google Kids Space on a second account when you're setting up a device.
As ever with updates there are plenty more bug fixes, minor tweaks, and optimisations, plus the usual collection of security updates to keep your device safe and secure. According to Google's schedule, some of the new features have already been delivered; the rest will arrive on 29 September via Google Play Services.