Comment 4 for bug 2063331

I guess we need a policy decision in subiquity: "Should it configure server NICs as <optional: true> or not?" rather than a technical fix here.

Longer term solution would be to somehow find a solution in cloud-init, not to block the boot process. But instead let the the systemd-networkd-wait-online.service timeout & fail while the rest of the boot process can continue in parallel.