It would be great to be able to play video files stored on an AirDisk : a USB hard disk connected to the Airport Extreme or Express.
FileBrowser or FileBrowser Lite offers this functionality, but only for some types of files (avi. Others?). For mkv fils, it gives you an URL that you have to paste in a media player.
It would be great to have this feature builted-in AirPlayer. Adding an USB hard drive to an existing Airport Extreme or Express would provide a very low cost "NAS like".