I think RH bet for neither of your options. RH recently bought Permabit, so dedup and compression should be available for current storage stack soon. ZFS/BTRFS management layer should be replaced with stratisd and udisk projects.
Instead of developing something "new" they opted to improve current stack (CoW for XFS) and add new features (Permabit) to achieve same or similar result but with stability provided by years of testing of current solutions.