A playlist has a shuffle button. Shuffles the items in that playlist. (Queuing disables shuffle, which makes sense.) Allow adding playlists to a playlist, which we can shuffle, and so get albums shuffled as well as tracks.
I’m not sure I understand what you’re trying to achieve?
I have a playlist for each artist in my music collection. Just the tracks I particularly like. Let’s say that while cooking supper I feel like listening to Fred, Albert and Mary. But I don’t want them in order, I want both the artists and the tracks shuffled.
A queue can’t be shuffled because adding to it while playing would be impossible, and other problems.
Playlists can be shuffled, so the solution is to be able to add playlists to a playlist, and that playlist can be shuffled-played.
EDIT: Even if it is a special, temporary playlist, a sort of special hybrid queue/playlist. Once play starts it cannot be added to.
How about a smart playlist or collection based on a set of artists and a track rating threshold?
You might want to take a look at Plexamp’s Mix Builder (though that requires a Plex Pass)
Collections could work with a track rating filter instead of a playlist. A bit of a schlep having to type the artist’s name, but can be done.
It would still be so much easier to create a (temporary) playlist containing playlists that can be shuffled.
But your suggestion will work in the interim. thanks.
EDIT: There is one problem - I will have to go through to my computer room and do it at the server. Sort of takes the spontaneity out of it. 
Just revisiting this thread and wondering… it seems this is actually already available in Plexamp.
You can add a playlist to the play queue just like you can add single tracks/albums/artists/…, using the Play Next and Add to Queue options.
