My main concern has been FileStore i.e. running an obj store on top of btrfs/xfs/zfs which even an armchair storage hobbyist (like me) can see, from first princ

My main concern has been FileStore i.e. running an obj store on top of btrfs/xfs/zfs which even an armchair storage hobbyist (like me) can see, from first principles, is a truly awful idea (journal-on-journal, etc). Bluestore will fix that at long last.