Hi and hello spotify!
Got an great idea for you!
What you need is a shuffle option that shuffles the music between all of the users playlist or selected playlists.
I don't think this suggestion needs any explanations, anyone can understand the positive aspects of this!
Many people sort their music in playlists by genre, mood, artist and so on and sometimes you just want it all random without being forced to change all the time.
The only alternative is to have a playlist with exactly all your other playlists in which takes up a lot of space in a mobile phone for a example.
My only demand is that this option would be named after me - "The Rydh Shuffle"!
I can come to an agreement of "playlist shuffle" but demands credits for my effort to write you this mail and give you this chance for advantage in the online streaming business!
Finally I would like to excuse myself for the perhaps badly written English.
I'm Swedish with no academic education in the English language department.
This is already possible:
If you want to shuffle all music you can just go to the library tab in the sidebar where all songs from all playlists are listed and use shuffle.
If you want to shuffle only certain playlists together, you can create playlist folders and shuffle the folder's music.
An idea to shuffle all music for mobile devices has already been suggested here:
Add your kudos there please! 😉