I'm not sure this buys us much. This can already be done within Ignition directly using replace.

Thanks for getting back to me so quick.

The replace directive allows a remote ignition config to be run.
However a config with this directive needs to be present prior to executing coreos-install.

In the instance you're installing from bare metal from the coreos_production_iso_image,
you either have to download the config, run coreos-install with this path or rebuild the iso with an ignition config present.

This will allow us to run:
coreos-install -d /dev/sda -i http://example.con/ignition.json

Sure it doesn't buy much, but it doesn't cost much either.