In Windows 10, Microsoft is not only improving how modern apps work on the desktop, but it is also unifying the modern environment with the desktop for a more seamless experience. Even more in Windows 10 build 9879, we can see a little more of this unification with the modern playback controls that now also appear for desktop apps.
In Windows 8.1, if you change the volume on a modern app, you will get the volume, plus the controls to play the media along with info and cover art on the screen. However, if you are using a desktop application such as Windows Media player, you will only get the volume control to appear on the screen.
Now in Windows 10, Microsoft is adding some changes and the same on-screen media controls that users see with modern apps will appear with desktop applications. However, in the preview version of Windows 10, you will only see media controls and not media information and cover art, but this may change in future builds.
Here are the Xbox Music media playback controls:
Here are the Windows Media Player media playback controls:
Another thing to keep in mind is that it seems that developers will have to include the support for media controls, as testing other media players, such as VLC, does not yet takes advantage of this new functionality.
Though this feature is mainly for touch-enabled devices, it will bring a sense of more unified operating system.