i wonder if it's really bricked?So, you're saying if you had Apple replace with a GENUINE sensor, it's brick? I don't think that is the case.
Also, in another life, I would reprogram chips for cars. The manufacturers were starting to reject these if modified. This is not new. The car would not start.
Given an replaced OEM sensor it doesn't function but can be synchs and work by Apple. It's not bricked.
How a 3 rd party sensor ever worked is beyond me. I think Apple found a security leak and fixed it in iOS 9.
Just replacing a OEM sensor was an issue known 3 years ago
2013:
"According to iMore, each individual Touch ID sensor is paired with its corresponding A7 processor. To confirm the pairing theory, iMore switched the Touch ID sensors from two brand new iPhones and attempted to setup each device. Each phone failed to recognize the sensors and returned an error until the sensors were swapped back to their original phones"
http://9to5mac.com/2013/10/31/the-i...print-sensor-is-paired-to-a-specific-a7-chip/