There's Talk Again About Btrfs For Fedora

[ryao]

Just as a data point, https://lwn.net/Articles/342892/ for a article from a former ZFS developer who notes some of the core differences, You already have several "conservative distros" using Btrfs including Oracle Linux and SUSE and they support it commercially. So if that is your criteria, ZFS and Btrfs has taken roughly the same time to be deployed in production and commercially supported and yes including as a root filesystem. So Fedora isn't the barometer in this matter despite its typically leading edge status.

https://lkml.org/lkml/2010/6/3/313 explains that btrfs has unbounded internal fragmentation. The author of the article you linked criticized ZFS' external fragmentation, but completely ignored the unbound internal fragmentation of btrfs. ZFS has ARC, which compensates for ZFS' external fragmentation. ARC also enables ZFS to outperform many other filesystems. btrfs simply becomes slower until either it runs out of space or is manually rebalanced. The manual rebalancing process kills IO performance while it runs. I am told that it is especially crippling on pre-SATA 3.1 SSDs when mounted with discard. To illustrate what I mean when I say btrfs can run out of space due to its unbound internal fragmentation, imagine a 256GB SSD formatted with btrfs that becomes full after only 25 gigabytes have been written.

As for having "conservative distros" use btrfs, I think people are more concerned about what the default filesystem is than they are about support for the filesystem. I am not aware of any major Linux distributions that use btrfs as their default filesystem.