Before /etc/machine-id, there was /etc/hostid.  It's kinda crap.
It is in glibc and coreutils, but only ZFS really uses it.

https://manpages.debian.org/bullseye/manpages-dev/gethostid.3.en.html
https://manpages.debian.org/bullseye/manpages-dev/sethostid.3.en.html
https://manpages.debian.org/bullseye/coreutils/hostid.1.en.html
https://manpages.debian.org/bullseye-backports/zfsutils-linux/zgenhostid.8.en.html
https://manpages.debian.org/bullseye-backports/zfsutils-linux/zpoolprops.7.en.html#multihost

    # systemctl start zfs-import-scan
    zpool: cannot import 'test': pool was previously in use from another system.
    zpool: Last accessed by alice-understudy (hostid=31a99d02) at Tue May 16 13:35:57 2023
    zpool: The pool can be imported, use 'zpool import -f' to import the pool.

With --include=zfs-dkms,zfsutils-linux you get an /etc/hostid in mmdebstrap's output.
I think /etc/hostid should be removed, like /etc/machine-id.
I think this would go under "cleanup/reproducible", like

        if (-e "$options->{root}/etc/hostid") {
            unlink "$options->{root}/etc/hostid"
              or error "cannot unlink /etc/hostid: $!";
        }