Because GStreamer is designed to be as generic as possible, a wide range of applications can be build on top of it. The example shipped with GStreamer is gstmediaplay , a simple media player that supports any media type for which plugins exist. This is usually done with racks of equipment and lots of cables, with a patch panel if you're lucky. Of course, just having the processing half isn't enough, which is why significant time and effort will need to be expended in the user interface and automation systems. A DVD player is a relatively easy thing to construct given the right components, some of which already exist.
Further work is necessary for the system to be capable of navigation, menus, and angles.
Just about anything you can think to do with media is probably possible with GStreamer.