I saw the implemented status of your request, as stated here: Version 7.2.0 released
Added a new Random (Stable) sort order for smart playlists. (Random is stable until you update the seed by pressing the asc/dec arrow to generate a new one)
I was also trying to figure out how this Random (Stable) logic worked as a way to choose a smaller subset of songs from a larger group to download them when I’m on the network of the server. I thought I’d share how I did it if others are interested in how this requested feature can be used.
I already had a playlist containing all the songs I want and then I created a smart playlist to go fetch a limited number of Random (Stable) items using “In playlist” filter. Other filters could be used here.
As OP said, when you change the sort order, the random playlist will refresh. If you set the smart playlist to be cached, you’ll therefore get new songs from the server.