1 November 2013iMore:
At this point, we knew there had to be some additional, previously undisclosed, hardware lockdown going on. To test this theory, we took two iPhone 5s handsets that had never been opened before, and verified Touch ID was working on both. The front assemblies, which contain the Touch ID assembly itself, were then removed and swapped. After re-assembly, both Touch ID setups failed. When returned to the original device, Touch ID once again operated correctly.
This confirmed for us that the Touch ID component cable assembly itself is tied to each individual A7 chip.
The amount of effort Apple has put into Touch ID is huge. You don’t put this much effort into something that doesn’t have a longer term vision attached.1
1 On the earnings call, Cook described this as the “front end of a long roadmap”.