I think it would be a great option to be able to always play the default lobby music, just by ticking a box in the settings menu or something. The default lobby music is a very chilling and relaxing track that fits really well with the atmosphere of the lobby area, in my opinion. Not only that, but with the constant events changing the music, it can be quite rare to get to listen to it at all (which is a shame, since it creates the best experience, I feel).
Doesn't sound like a complicated feature to implement either. I have a feeling a good amount of players would enjoy this being implemented, but please let me know if you do think so. The more of us actually show interest, the bigger the chance this becomes a thing.