I was thinking about something very, very, similar. It would do almost exactly what I want. (Maybe exactly -- I'm too lazy right now to actually think it all the way through. )

The only issue I can think of right off of the top of my head is when you insert something in the middle of a playlist, so that an initial group is split in two. I think the best thing would be to keep track of where the ends of playlists are (the same thing as a boundary, really), and the command would be something like ``skip to end of current playlist''.