I think that people are overcomplicating things. Virtually the only thing you have to change to automount btrfs sdcards is to remove the uid=X,gid=X settings from the mount-sd.sh script. This is a much simpler modification that what people are doing over that thread, which is probably the result of a misunderstanding of some kind. Additionally, I suspect this change will come with a future SailfishOS update. Everything -- including Tracker and thus the Music application -- works afterwards.