As the original article mentions, it sounds like Apple has already engineered a situation where they can't get into their own phones. This Apple only backdoor option exists only in equipment that predates the secure enclave hardware (such as the phone in this case).
The only way to bypass the brute forcing delay would be to increase computing power, since it's a function of the encryption method used. It basically goes through a number of iterations chosen to make it take about 80 ms per attempt.
They always can. Microcode updates come to mind. While apple have the ability to keep their ecosystems locked, they also have the capability to unlock them.
Probably not easy and not on mass scale. It may even need to have to see inside the silicone itself. Which is expensive and hard. But as long as the keys are on the device or in possession of apple - they can be extracted.
Worse case, you disassemble the die and read the bits off with an electron microscope. It's still possible, just expensive, painful, and maybe dangerous if you damage the chip.
