I formatted my sdxc 64Gb card to Btrfs -filesystem in Jolla. Everything went okay and after manual mounting happily moved all my music and pic files back to card from /home/nemo/...

I also changed the /usr/sbin/mount-sd.sh script according instructions in Jollausers.forum (it might be also here in TMO) and now the mounting of btrfs-card does not fail when rebooting.

Jolla SD card

I still have to make a soft link from sdcard to Music and Picture folders to be able to use them with Media or Gallery. Maybe some update will fix this one.