Detailed app permissions control might be debuting in Android M
One of these might be granular, user-manageable app permission controls. All versions of Android after 4.3 Jelly Bean have allowed users to grant or revoke app permissions after they've installed a given app, but this functionality is deeply hidden in the OS itself and can't be accessed without a third-party app, with the most popular being App Ops (requires root for certain versions), making it a bit tricky to access it.
Android M might finally bring this undoubtedly handy feature up front and allow users to manage permission to their heartfelt content. There might be a dedicated menu in Settings that deals with app permissions. Also, it's rumored that on the next versions of Android, you won't need to grant various permissions before you install an app from the Play Store, which is a slightly cumbersome task that usually requires you to tap "yes" in a handful of dialogs.
While it's not certain, there's a possibility that in Android M an app could ask for permissions right before you start it, similar to the iOS take on the matter. Yet, it's not certain what will happen if a user denies a core permission to a given app. We will have to wait in order to see what these app permission might be and whether they'll land on Android at all.