The ability to use the desktop app interface to play songs (via Spotify Connect) on a remote device, i.e. wireless speakers. Cannot believe this is absent right now, as it seems pretty integral to the whole idea of Spotify Connect (who actually uses their mobile as their primary listening device while in the house?!)
A secondary suggestion would be to add that functionality to the web app also.
Note this is not a duplicate of the feature request at https://community.spotify.com/t5/Spotify-Ideas/Spotify-Connect-For-Desktop-App/idi-p/689688 titled "Spotify Connect For Desktop App", which referred to controlling the desktop app via a remote device i.e. the opposite way round, and has now been marked as implemented.
Hi, a similar idea has also been suggested here:
Add your kudos and comments there please!