I never did try and convert my existing ReadyNAS to it (there are unofficial ways to do this, but it involves a full factory reset).

RHEL 7 is switching from ext4 to XFS as the default. BTRFS support is advanced from the experimental preview in RHEL 6 but didn't make the cut to be the default. Being that they are a bit more conservative, this tells me that it's not quite ready for primetime still on something highly mission critical, but may be fine in general use elsewhere.