I understand what you want to do, as of current there is not a cmd that loads all music into a playlist. The closest & fastest work a round right now is to go to browser>search>all then just enter a space, when that gets done, click the manage playlist btn and add the [searchresults] to a disk(and rename to All Music if want to). This does a few things, #1 puts all your music on disk so you don't have to do it again, #2 you can add songs from one disk(currently loaded) to anther disk, #3 when you decide to play something else for a while and then want to go back to look for more songs to put on another disk, loading the All disk will jump you right back to where you were when you left it..
This is the second time the problem with how does one add all music to a playlist came up, so I might just add a single cmd that would do this instead of the work around.
Will put on the low Priority look into list.