I've seen this suggestion written a few times on the Discord, for whatever reason, I just don't like the idea. It's all immersion breaking.
Most people in freeplay will now just pick their favorite tracks, and will disregard the others. Wouldn't it seem the unpopular tracks would slowly just become used less and less? It breaks the immersion. We don't hear rainforest sound effects in the beach maps, it'll be weird. What about, we say, you have the music disabled, so what's the point of having this option? It would take some time to put this feature in, and almost everyone has YouTube now, use that to play custom tracks.
I think my biggest issue with this is the immersion it will break. Although, anyway, right now; the game needs to be finished. This is something post-early access, and I think the developers should just slowly check off things from their roadmap, and listen to the community after the game is completed. I think that will be the best move.