I have been performing upgrades as normal with the previously mentioned line commented out in /usr/lib/initcpio/install/kms. All updates that have prompted image rebuild have been successful. Have not yet noticed any side effects from this workaround.
(5/7) Updating linux-rpi initcpios...
==> Building image from preset: /etc/mkinitcpio.d/linux-rpi.preset: 'default'
....
==> Image generation successful