New commits submitted to the Android Open Source Project (AOSP) seem to suggest that a future version of Android will offer native support for using an Android device over Bluetooth as a human interface device (HID). Specifically, the new commits point to the enabling of HID device profile service. For those that may not be aware, the most common use of that particular profile service is often associated with Bluetooth keyboards, mice, or gaming controllers. It goes without saying that the Android platform already supports the use of those kinds of devices in conjunction with Android handsets and tablets but this particular set of commits seems to enable the use of an Android device as an HID itself. That could mean that a future version of the OS would allow an Android-powered product to work as a Bluetooth input device for other Bluetooth-enabled hardware. For example, a smartphone with an enabled HID profile service would be able to act as a keyboard and mouse for a PC.
The timing of the addition suggests the feature could be part of the upcoming Android P update. Google is expected to unveil the new OS no later than at its I/O conference in May. So it may not be much longer before Android users have yet another feature to ramp up their own productivity. Obviously, the use of an Android device as a Bluetooth mouse or keyboard has been possible for quite some time. However, the capability wasn't previously included in the native Bluetooth stack and more often than not required a rooted device, which is arguably a lot of effort to go through just to be able to use a tablet or handset as a wireless input device.
If the functionality does launch alongside the next iteration of Android, it would effectively be available for use by anybody running the OS on their device. There are, of course, a ton of other features expected to be added to the next iteration of Android, many of which are said to be focused on reducing the overall fragmentation of Google's mobile ecosystem.