Google has recently released the Android Compatibility Definition Document for Android 7.0 Nougat (finally !!), and it definitely contains a lot of surprise such as the ability of the firm to update a piece of Android without the concern of the manufacturers.
It is that particular paragraph, paragraph 3.1.1 that catch the interest of ArsTechnica. According to them, that paragraph stipulates that Google will be able to update APIs found in AOSP (Android Open Source Project) which is the core of Android to which Google add his own services to the Google Play Services.
Getting into details, it forces manufacturers to implement the libraries “ExtShared” and “ExtServices” coming from AOSP who won't be able to modify them. These new system apps (APKs for now empty) installed by default on devices equipped with Nougat will be updated directly by Google through the Play Store.
With this, Google wants to increase the number of items it can update through the Play Store. Today Google can update it apps (Gmail, Keep, Now Launcher etc) through the Play Store as well as the Play Services without the approval of the manufacturers. Here, Google will be able to update a set of APIs coming from AOSP. These APIs correspond to those of newer versions of Android whose source code is open compare to that of Play Services which is close.
We can therefore understand that Google would also want to make available some new features found on newer versions of Android on older versions. However, this does not means that Google will exclure major updates of Android, some of which doesn't reach some phones either because of technical problems or refusal from the manufacturer or telecom operator.