Re: Lack of imagination?
Five minutes after the head of the FBI has such a key, so do the Chinese. And the Russians.
And the Indians, Malaysians, Europeans, Iranians, Italian Mafia, Columbian drug dealers and every other organisation you might care to mention that has a reasonable amount of money coupled with a desire to get the data from someone else's iPhone.
Within a couple of years, every script kiddy in the world has a copy.
That's the reason it's impossible.
Think upon this - if such a God Mode key is brought into existence, it would be one of the most valuable pieces of data on the planet. Some people will gladly torture and murder to get it, while others will willingly pay said people rather a lot of money.
The more widely distributed, the sooner these people would succeed and the more agents would be put at pointless personal risk.
If I were an FBI agent, I would not want this, because I would like my and my colleagues limbs to remain attached and fingers unbroken.