A page or feature that allows you to shuffle multiple artists together. This could be in the form of an addition to the Playlists feature (the ability to add a whole artist's page, i.e. all of their songs, to a playlist) or as an ability to create an Artist Radio where you select multiple artists to create the station. This could be useful for creating more user-curated music collections-- if you feel that multiple artists or bands play well together, you could add them into a mix, whether that be artist radio or a large playlist.
This could also help in creating "Ultimate Artist Playlists." If an artist you like also features in a band or multiple bands, you could add the solo artist's discography as well as the band/bands's discography to the playlist or radio. For example, an Ultimate Paul McCartney station could be created by adding the Paul McCartney's artist page or discography along with the page for The Wings and the page for The Beatles. If you like the sound of Gorillaz, you could add together Damon Albarn's page, the Gorillaz page, The Good, The Bad, and The Queen page, and the pages of any other frequent Gorillaz collaborators you enjoy the sound of.
Ultimately, this feature would create an expanded and more convenient customizability of playlists and/or artist radios for Spotify listeners.