> - easy storage management, the "rampant layer violation" of zfs we really need;

Except in zfs you have to think if you really want that device in that pool or that vdev. I use btrfs, slow and kinda unsafe, specifically because you just specify raid1c2/raid1c3/raid1c4 and it kind of survives c-1 dead disks (until you run out of disk space and everything goes to flames).

> - integration of such storage to the software stack, from the OS to single packages, it's a nonsense having to "spread" archives in a taxonomy to deploy them or downloading archives to be unpacked as well for updates when we have send-able filesystems (zfs send of snapthots) and binary diff (from a snapshot "tagged version" of a fs-package to another, sent over internet).

We (kinda, for some very generous definitions of) have that in composefs? But I still sense even with that, you still want some resemblance of sanity in your indivual layers.