[brk]

This was my thought too after reading this article.

Part of this relies on the specific iPhone 5c from the shooter, because of the per-device hardware key. They ultimately need to unlock that specific phone, with the NAND data intact, in order to read the contents.

But, if the passcode is stored in NAND and validated only against user input they could duplicate the NAND and parallelize the process. If any part of the user code check involves the hardware key, then it wouldn't work.

[m_mueller]

In the article it is specifically mentioned that multiple keys are used for the encryption. There is a secret key burned into the A6 processor that is hard to access without the risk of destroying it. This key cannot be destroyed programmatically, so a secondary key on the NAND is destroyed in case of too many attempts. Only that process could be circumvented with this technique, it doesn't address the increasing interval and AFAIK it is not possible to multiply the hacking process without somehow multiplying the A6 chip - i.e. very hard.