I believe drivers/staging should be renamed into fs/staging, since this tree will likely contain CEPH and NILFS2, as long as POHMELFS and DST.
Ceph is a distributed file system designed for reliability, scalability, and performance. The storage system consists of some (potentially large) number of storage servers (bricks), a smaller set of metadata server daemons, and a few monitor daemons for managing cluster membership and state.
It relies on BTRFS to store data and closely works with its internal features like transactions and cloning.
NILFS2 is a log-structured file system supporting versioning of the entire file system and continuous snapshotting which allows users to even restore files mistakenly overwritten or destroyed just a few seconds ago.
NILFS2 lives in -mm tree for a while already, so this actually may be a call for the mainstream inclusion directly into fs/.
More filesystems – good and different!