So, the installation media presumably ships with a public key baked into it, which the firmware picks up and installs, and then we proceed to boot the installer. The private half of that key really needs to not be on the installation media, otherwise the bad guys can grab it and use it to sign malware. But we want to end up with a private key — a freshly generated one — in the user's possession, otherwise people who need to build their own kernel or bootloader (for whatever reason) are hosed. Can we arrange to generate that key at installation time, write the full keypair to a USB stick, and the public half to the firmware, without requiring an extra reboot?

Also, in very tightly controlled environments the sysadmin might want to wind up with only their locally-generated private key trusted by the OS, but I think I'm okay with that use case requiring the sysadmin to generate a custom installation image. They're probably doing that anyway.