Okay, this idea has been requested and liked many times yet still years later nothing has been done so I felt the need to post again.
All we want is to be able to select multiple playlists, and have our mobile app shuffle through songs in all the selected playlists.
I understand mobile app / app development in general, and this really is a very basic and easy feature to add with absolutely no drawbacks and would make a lot of people happy.
Currently, we have to make a redundant playlist and add all our songs to that one in the case we want to listen to all of them, and then if we add a song to any of the other playlists, this one needs updating manually, it's messy.
I hope you consider this request,