It's also been the default for the root filesystem in openSUSE since 2012. It also integrates with the package manager - zypper creates pre- and post- snapshots when installing updates, and the snapper utility makes it easy to roll back if your system is busted after installing an update. It's saved my bacon on multiple occasions.

(btrfs also used to be the default for /home, though that changed at some point. When I made a new install last year the installer suggested xfs by default.)