I would love to have music integrated in the application.
Long sessions, already over 1/2 hour, can be boring. Having music, possibly your own, would help to pass time and keep concentration.
These could be the requirements:
Music BPM should match the cadence you should keep for a give training. You should have an algorithm to resample the music to change its BPM
The user should be given the option to upload its own musical pieces/play list
music should be optional
you should be able to change what your are currently listening
music should fade when someone is talking to you (e.g. ride on, etc.).
Am not sure it would get used that much, as for people putting their own music on just wear a pair of headphones? there is no need for zwift to have the function of uploading mp3s etc
Spotify or similar account playing on another device or same, keep the clutter off of the Zwift game interface. I have 2 separate playlist setup, biking and running.
Due to the cost associated, it would be extremely unlikely that we would look to integrate with (eg) Spotify or look to build in playlists to align with your heartrate.
Mainly, what you are asking for could be managed by using your own music.