Ok, and that is actually one option the FBI asked for. To take down the limit of guess before the phone erases the content - and they will brute force into it - but Apple wont even do that. By the same logic the government would not use that much time and energy to get into aunt Betty's phone for no good reason.
That's pretty much THE option Apple has been given by this court order. It still requires significant effort on Apple's part to develop the code that will override this setting, and to test it thoroughly to be sure their solution doesn't brick the phone permanently, or trigger the safety so that the decryption key gets deleted.
I guess if they do brick the phone, they can do a factory reset and then restore it from the latest iCloud backup...
Now, this phone is secured by only a four-digit passcode. We know this presumably because when they swipe right, they see four blanks in the passcode entry screen. My phone is also secured with four digits. It's convenient and easy to remember. I don't worry so much about someone brute force trying to guess the code because the iPhone locks after several wrong attempts. My nephew tries sometimes. He brings the phone to me after the phone is locked. At three years old, he's not much of a threat.
If Apple is forced to comply, and removes the delay (and the "erase phone after ten wrong tries" option) it won't take too long for the FBI to go through all 10000 possibilities. At one try per second, that would be less than 10,000 seconds.
We already know that the DOJ has more phones waiting in the wings for Apple to do this same trick to. But do we know whether all of them have 4-digit passcodes. Apple's default length for passcodes is 6 digits now. That would take 100 times as long, or 1,000,000 seconds (more than eleven and a half 24-hour days). And Apple also has an option for longer alphanumeric passcodes. It would take decades for the FBI to try all the possibilities. Whatever data was on the phone would probably be useless by then.
If Apple loses this case, don't you think real criminals are going to start using the alphanumeric passcode option on their phones? I'm thinking I will go to alphanumeric, and I'm more worried about my nephew getting in and accidentally deleting an important email or calendar appointment than I am about the FBI.
With criminals (and innocent people who might happen to be accused of crimes) using stronger passcodes, this method is going to have limited usefulness for the FBI/DOJ. On top of that, Apple has already strengthened the security on their iPhones. Any iOS device that has a fingerprint reader has the code for delaying after a certain number of bad attempts moved to the "Secure Element" chip where the fingerprint data is stored. A mere iOS update couldn't override that code.
Future iPhones may not allow updating the iOS using DFU mode without entering the current passcode, so loading a new OS to allow guessing the passcode won't be possible unless you already know the passcode.
The point of all of this is to make the iPhone less hackable.
So if this is not going to work on newer iPhones, or when the user has chosen to use a stronger passcode, why is Apple fighting this one case? It's because if Apple can get the courts to agree with them that making the iPhone more hackable is not a Constitutional request that the government can make of Apple, then they'll be better positioned to resist future requests from the government to make the iPhone more hackable.
They're still going to fight those future requests, which will be asking Apple to do more and more to get around the bigger and bigger roadblocks Apple has put in place to keep out cyberterrorists, identity thieves, and spies. But a win in the beginning will be a precedent Apple can point to in future cases.