After playing with BTRFS and using grub-btrfs, though this may be an error on my part, I don't recommend booting from snapshot using grub-btrfs. I've had to reinstall my setup 3-4 times when playing with booting from snapshot and then trying to go back to my non-snapshot system. Things including init(s6) would cause me issues upon logging in; Such as not being able to obtain s6 lock.