Re: Why is this even necessary? "counterfeited in a VM..."
Mmmm, I don't think so. As mentioned before, even in the 5C iPhones without Secure Enclave, the passcode is combined with a hardware-generated key -- and that key would not be known to a VM. From the TrailOfBits blog:
"Devices with A6 processors, such as the iPhone 5C, also contain a hardware key that cannot ever be read and also 'tangle' this hardware key with the phone passcode."
To recap, the phone will erase everything (actually, it will permanently "lose" the encryption key) if the passcode is incorrect for more than 10 guesses. Only Apple can flash the firmware for the phone, and the FBI wants them to flash a special iOS system which will overwrite the limitations on brute-forcing. In that case, according to TrailOfBits,
"However, there is nothing stopping iOS from querying this hardware key as fast as it can. Without the Secure Enclave to play gatekeeper, this means iOS can guess one passcode every 80ms."
At least, that's what I think I get from the tech explanations.
(If it was as simple as jailbreaking the phone, or pulling the guts and hooking them up through a VM, it would have been a done deal a long time ago. The FBI are not THAT stupid.)