Currently, when you select multiple playlists there is only one option “Delete” (besides deselect all). I would like to be able to shuffle play two or more playlists. Another/a partial solution would be to select multiple playlists then be able to “add to new playlist” thereby creating a new playlist with all the songs from the original playlists. The only way I can find to do this (besides re-selecting each song individually) is to play a playlist, go to the second playlist, select add to play queue, then go to the play queue and add save the queue to a new playlist.
Early 2021 clean-up: implemented (e.g. shuffle, play next, add to queue – no option to add both to a new playlist in a single step though)