It's quite the opposite in fact. BTRFS was pulled INTO the kernel recently. It's seeing massive development and is production-ready.

> Why not ZFS?

The main reason for me is its flexibility. Just an example: Expanding BTRFS is just a matter of shoving in arbitrary disks and rebalancing the existing array. ZFS requires you to plug in drives of the same size to properly scale.

I wrote about this some time ago, in case you're interested: https://garrit.xyz/posts/2021-02-07-storage-setup