Google has been sending out emails to developers whose apps use Android's built-in accessibility API stating that any apps that do so in a manner meant to do anything besides help users with disabilities will have to change the offending behavior, or risk being de-listed from the Play Store. The accessibility API built into Android allows for things like onscreen overlays on other apps, intercepting button presses and taps, and other deep system-level behavior. Many apps having nothing to do with disability are powered by this API, including apps that can help users to customize their devices' functionality. Developers of these apps have one month to comply, or see their apps taken off of the Play Store. This leaves a mark against a developer, which can result in consequences up to and including closing the developer's account and banning them from Google Play.
The email seems direct enough, but it actually seems to contradict Google' existing policy surrounding the use of accessibility services, which states that the purpose is to help users who may be permanently disabled, or temporarily unable to interact with their device in a normal fashion, such as while driving. A note popped up on the policy page somewhat recently, however, that directly contradicts that; the note specifies that the accessibility API should only be used to help users with disabilities to interact with a developer's app. This technically means that helping users to interact more easily with their device in general, whether they're disabled or not, is no longer a permissible way to use the accessibility API.
Currently, hundreds of popular and useful apps in the Play Store use the accessibility API in ways beyond this descriptor. Nova Launcher, one of the most popular apps in the Play Store, uses the accessibility API to listen for notifications, among other functions. Battery saving apps, apps that allow you to customize button functions in any way without root, and apps that overlay something on the screen, such as Button Savior, all fall under the purview of the new ban, to name a few. This means that these apps will have to transition such behaviors to a root method, putting strain on developers to transition, and taking these functions away from the many Android device owners who don't want to root, have devices that can't be rooted, or don't know how to root.