Posting this issue on someone else's behalf.
While playing with GRUB on X86, I discovered a couple of unpleasant things, when combined cause a real headache/nightmare:
1) After selecting 'ONIE' in GRUB, it defaults to ONIE Install mode and before you can read all the text the first time (i.e. 4 seconds), it executes ONIE installer
2) ONIE installer loads. Then there isn't a fast easy way (at least no instructions on the screen...anxiety rising..) if any exists, to abort the autoloading/install of the default image via the waterfall (onie-installer-x86_64 found very quickly via the local webserver)
3) While unsuccessfully trying to stop the ONIE install, you watch with horror as ONIE downloads and installs a new OS, overwriting the existing setup. Again, no way I could figure out how to stop that either....
Net result, you have whatever default image is configured on your webserver, and all vestiges of the config and license on your functioning switch has now been erased and must be restored from backup.. you did create a backup.. right?
I would propose that in GRUB, when you go to the ONIE page, that GRUB not be set to autoexecute ONIE Installer in 3 seconds.
I would further propose that an abort sequence be accessible and printed to the screen when ONIE Install mode starts that would allow halting the install for at least 10 seconds after ONIE loads.