* Support for multi-volume btrfs filesystems
* Support for other mkfs.btrfs options, if any are useful.
* Support for btrfs snapshots / using existing btrfs?
* mountoptions is missing a few options that may be worth supporting,
  including degraded, and all options that require a parameter.
* mountoptions contains nobarrier, which is an unsafe option. Remove? Warn?
* Resizing?

* How about installation into different subvolumes?

  Example:
  / (root), /usr, /var and /home each on the same btrfs filesystem,
  but as separate named subvolumes (root/default, usr, var and home).
  
  This would break the one filesystem==one mount concept currently
  used by the partitioner.  Here, one filesystem would be mounted
  in several places, but with a slightly different subvol mount
  option.  Maybe handle like LVM, where there's a separate dialogue
  for creating LVs (subvolumes), and then select individual
  subvolumes on the main partitioning dialogue for mounting in a
  given location.