so i heard you wanted a filesystem that is copy on write, in-tree (so not zfs), does not eat your data (so not btrfs) and is not maintained by a certain person (so not bcachefs)?
i present you, ocfs2, or oracle's cluster file system version 2
you say that it's for shared network disks in clusters? here i put it as a root filesystem, on a core 2 duo thinkpad, running off a single usb stick on usb 2.0