This feature appears to be completely nuked in the latest desktop version (I'm on OSX).
Typically, my usage pattern is to queue up a bunch of music and forget about it. When I double click a song, it will stuff the Play Queue with a bunch of stuff I don't want to listen to. Before, I had the option to swap out the Play Queue with songs from another playlist using the "Choose as current playlist" feature (so when the stuff I queue up is done playing, it will switch over to the playlist). I also use this feature to indicate that I don't want any songs to play after the things I've queued up (by choosing an empty playlist as the "current playlist").
Without this functionality, the Play Queue is stuck there. Yes, I can doubleclick a new song somewhere else, but that will interrupt the song that is currently playing. In general we need a better way to manage the music that autoplays after the queued songs.
Hey guys, we're marking this idea as 'Not Right Now' for the time being. However, we're continuing to bring your feedback to teams internally every week. If there's an update on this decision we will let you know here, thanks everyone.