Does btrfs-zero-log work only on a single partition or can it handle BTRFS filesystems spanned across several devices?
LVM functionality is only partially replaced by BTRFS
One thing about LVM Volumes in contrast to btrfs sub volumes is quota's. Every LVM VOlume has a hard quota and if it runs out of space other volumes are not running out of disk space. This is one functionality that btrfs has not (yet) implemeted.
For this reasson I stil use LVM, but with btrfs filesystems in the volumes and not with ext4 (anymore).