Those "legacy constraints" are often being used. Backwards compatibility is very important, because throwing out decades of development efforts involving millions of man-hours. Supporting legacy interfaces can be annoying and in some situations it gets in the way of newer features, but it's incredibly rare
> ZFS
Nothing needed to be thrown out to implement ZFS. More than one software interface can exist at the same time. ZFS development didn't use some of the features used by traditional filesystems, but it's "rampant layering violations" didn't require the removal of UFS, RAID, or older volume management drivers. The fact that it's always been possible to mount ZFS and older UFS disks at the same time should make this obvious.
I'm only talking about software.
> legacy constraints
Those "legacy constraints" are often being used. Backwards compatibility is very important, because throwing out decades of development efforts involving millions of man-hours. Supporting legacy interfaces can be annoying and in some situations it gets in the way of newer features, but it's incredibly rare
> ZFS
Nothing needed to be thrown out to implement ZFS. More than one software interface can exist at the same time. ZFS development didn't use some of the features used by traditional filesystems, but it's "rampant layering violations" didn't require the removal of UFS, RAID, or older volume management drivers. The fact that it's always been possible to mount ZFS and older UFS disks at the same time should make this obvious.