Samsung phones blow e-fuses when you unlock their bootloaders, so there's no going back. I think this would prevent a proper GrapheneOS installation.

Perhaps Samsung could start shipping phones with GrapheneOS natively installed, but since the phone's owner would not have control of the OS, that would arguably not be GrapheneOS as we know it today. Or maybe Samsung could change their chain of trust implementation to be more like Google's, allowing the bootloader to be re-locked.