The best resource for Chrome hardware is https://mrchromebox.tech/#devmode.
It seems like getting to a shell in order to install alternate firmware requires having ChromeOS installed. It is possible to create USB flash installation media using the following script and list of devices:
- https://dl.google.com/dl/edgedl/chromeos/recovery/linux_recovery.sh
- https://dl.google.com/dl/edgedl/chromeos/recovery/recovery.conf
I didn't trust running the script with super user privileges so I ran dd manually as follows:
sudo dd bs=4194304 of=/dev/sda if=/tmp/tmp.crosrec/chromeos_12371.75.0_pyro_recovery_stable-channel_mp.bin conv=sync status=progress
I had to remove the SD card I had inserted into the Chromebook, but it still would not recognize the USB drive. For some reason another USB drive was recognized. You can test this by plugging in the drive at the screen with the yellow exclamation mark.
In developer mode at the screen with the red exclamation mark I hit Ctrl-D, signed into my Wi-Fi network, switched using Ctrl-Alt-F2 to another virtual console. I logged in as chronos and followed the steps to install the firmware.
https://wiki.archlinux.org/index.php/Chrome_OS_devices#Installation