So basically the server can send a request to YouTube and play a song server wide that the players can /callvote song song here and admins can !play song here and the song will be played for the in game players. Song can be ignored with a modified /ignore song or something. Clients can have their own Music sliderbar to control volume which could be compatible with other various trem features such as waiting music. While this would take quite some effort, it is very possible to add.
There could be copyright issues with using YouTube for this kind of feature. But I have seen some servers on Xonotic offer music pk3 files that the server would signal to play. If you didn’t have the next song that was going to be played, you would actually download the missing pk3 while playing without interruption.
I do not see any foreseeable issues with this. It is obviously not monitized, and it isn’t any different then that of someone playing music in the background. It would ba akin to someone saying “alexa, play whatever”. Besides, i have seen other games implement similar this (with slight differences). The only issue I could see with this is someone filming a game and having the music in the background whereas that WOULD be a big issue, however they could just shut off the music
Could list the games that you are aware of with a similar feature? Do you know if any of them are open source games (which might make it more straight forward to port over)?