s390x doesn't support the QEMU firmware config device that we use to pass Ignition configs through to RHCOS guests. As a fallback, libguestfish was used to modify the root disk to directly inject the Ignition config. This doesn't work on remote machines though(as is always the case with libvirt and the cluster API provider), so the new approach is to use the RHCOS images built for OpenStack and to pass the Ignition config through the config-drive mechanism instead.
Verified by Xin Ke Wang <email@example.com> from the IBM Z team.
Moving to Verified.