I need this feature too! I'm writing a web app that can generate dynamic playlists. It generates X songs and queues them up, but if the user changes their mind I need to remove those songs from the queue.
The queue system in general is pretty borked. I was pushing things to my queue from my app all day yesterday . . . got in the car and played a new playlist and I ended up having to fast forward past like 20 songs that I'd added via the app, even though I had cleared the queue via Spotify an hour before!
That would be awesome! Waiting for this endpoint for over half a year now. I've built an app that lets users add songs to the queue via IRC. Since it takes the first result from the search, many times moderators have to manually skip misspelled songs. Lettings users remove their own songs from the queue again would be a great improvement.