A <playlist> tag for audio playlists, most importantly in M3U, would be very useful. It would work as follows:
<playlist name="Broadcast"> Broadcast1.mp3 Broadcast2.mp3 Broadcast3.mp3|My favorite song Bad-Url.exe </playlist>
My favorite song
File not found: Bad-Url.exe
These would have to exist either locally, or in the shared repository (Commons or similar).
The "Play back the following files:" link would point to a title=pagename&action=m3u&name=Broadcast&extension=.m3u URL which would send back an M3U file with the full URLs of all the valid filenames (one per line) in the playlist specified with name. The action would have to return a page of the type audio/x-mpegurl.
The extension=.m3u is necessary because some players only recognize an M3U as such if the URL contains the extension. URL rewriting might be used to accomplish the same effect. For security reasons, &extension=... should accept no other value than .m3u, and be only valid in combination with the m3u action.