Nope, because everything is ultimately dependent on the hardware key in the Secure Enclave and the user's passcode, neither of which Apple has knowledge of. The FBI would be able to create the OS, but they wouldn't be able to load it on the device without erasing it. It's really a brilliant system.

Compelling production of Apple's private keys would (for better or worse) be a far easier legal question than what this subpoena seeks to compel. Remember the Lavasoft case? The private keys were ordered produced there. The difference here is that what is sought to be compelled here doesn't exist now; it will have to be created through expert engineering and software design work.