For me you have taken a very appropriate approach, targeting VM creation which is well in line with what I suspect are the mainstream uses for CoreOS. Thank you for your work on that - it is very cool. Speaking as someone who has not had any long term experience with CoreOS, it seems it would not make sense to adapt it that to a very different bare-metal install scenario.
For me, I got very frustrated with installing CoreOS onto custom or finicky or non-standard (non-virtual) real hardware. It seemed that anything beyond common settings (network, users and hardware), where a config needs tweaking to see what works, can get very frustrating and time consuming. Felt like an old fashioned “batch” approach - create the fcc, compile it, boot the live iso image, copy over the config, install the OS, boot the OS, see what works and didn’t, repeat - often.
I suspect that a config tool running on the actual target hardware within the context of a booted live image would be a better approach to solve that. Or at least something that could take a snapshot of selected environment parameters to produce a coreOS image would be helpful. But I am not sure enough folks have this issue for it to be a worthwhile effort. And all this is outside the context of the issue your tool is addressing - so apologies for that