Break the linear flow of a playlist by allowing users to queue specific tracks out of playlist order, jumping between points in a playlist.
This behaviour is implemented in Amarok and Audacious, possibly others, but I haven't seen it done for an MPD client.
I am not familiar with the Ario or MPD codebase, but I could imagine it operating like so:
* The Ario playlist in the client is populated with entries from the user and from communication from MPD, but is not the playlist sent to MPD.
* The playlist sent to MPD is separate and hidden from the user playlist, dynamically created from user interaction.
* When a user 'queues' or 'dequeues' a specific track the track order on the dynamic playlist sent to MPD is altered.
* When a user clicks 'stop playing after track' the dynamic playlist sent to MPD is cropped to this single track.
This system could also be used to queue playlists too.
I'm currently working on another project but if I get a chance I'll see if I can hack something together.
Thanks for a great MPD client.
A server side implementation was previously discussed here: http://mpd.wikia.com/wiki/Talk:MusicPlayerDaemonQueue
Amarok implementation: http://userbase.kde.org/Amarok/Manual/Playlist/QueueManager