IANAEP, but my algorithm would be pretty simple. If all of the MP3's in a playlist have an attribute in common, the playlist gets assigned that value for that particular attribute. So if you've got eleven Pearl Jam songs in a playlist, the Playlist Artist would be set to Pearl Jam. If those songs happen to all be from the "Ten" album, then the source for that playlist would be "Ten." The Genre and Year would probably then be the same, so those fields would be set accordingly.

Similiarly done if you've got a playlist full of songs from 1963, a playlist full of songs which are all in the Christmas genre, etc.

The only argument against implementing this feature is that soup views are coming to the player, to which I would respond "yeah, but where are they?"