The hard drive content is encrypted. Assuming there are no backdoors, seems like the only thing they can try is to make bruteforcing easier.
His intentions: good. His success probability: unlikely (unless they have knowledge of how the encryption key is built from the passcode)
Source: http://www.businessinsider.com/john-mcafee-ill-decrypt-san-b...
"Mr. Cook, it's John McAfee on line three, again. He says, quote, 'pretty pretty please.'"
My original question still stands
It does seem that if the FBI desoldered the security chip and subpoenaed the KDF algorithm, they could recover the raw encryption key using their own hardware. But perhaps I'm missing a detail.