Google’s updated Compatibility Definition guidelines state that OEMs won’t be able to mess with Android’s notification system from now on. This means that, no matter what Android phone you buy in the future — as long as it’s running a new version of the OS, of course — it will handle notifications the same way all other Android devices will.
Specifically, this means that notifications will be grouped together in the notification shade and users will have the option to reply directly to messages from their respective notifications, as it is the case in the latest … – Source
Notification grouping and direct replies to become mandatory in all Android OEM skins