The Bluetooth SIG has certified another small update to the Windows 10 Mobile Bluetooth Stack.
There are only two differences between this stack and the one which shipped last year.
The first is that the Audio/Video Remote Control Profile (AVRCP) has been updated to version v1.4 from version 1.3. Microsoft has already said they will update this further to version 1.5, which will bring the ability for devices to browse and search media and playlists on devices and support for Absolute Volume, where turning the volume control on your head unit would adjust the volume on your phone.
Another change however is that Windows 10 Mobile can now both act as a Audio/Video Control Transport Protocol (AVCTP) target and controller.
It could always act as a target, meaning for example your Bluetooth headset could advance tracks and pause and start music on your phone.
Now with controller capabilities, your phone should be able to connect to a Bluetooth stereo and control music playback without actually being the source of the music, similar in principle to how a Chromecast works.
The changes will likely ship with the Windows 10 Mobile Anniversary Update in July.