That's just silly. First, Apple's already made clear that they'll take care of an issue resulting from a broken device that hasn't been serviced by an unauthorized shop. Second, it's a bit unrealistic to expect the system integrity checks to necessarily be able to determine whether something is out of spec because of a broken component or because of the installation of a bogus component. If there is uncertainty in that regard, the default has to be the assumption that the integrity of the 'enclave' has been violated. There's no subterfuge there. That's how security works.
The TouchID device is sold with the assurance that fingerprint data does not leave the device, but rather remains in the secure 'enclave' that exists from the surface of the reader to the hardware that stores and then verifies the fingerprint of the user. The level of security being sold with this feature means that no one - including Apple - has access to the actual fingerprint data.
The moment Apple allows even for the possibility that the fingerprint data's chain-of-custody could be violated, then the whole thing becomes effectively insecure. If the system integrity check defaults the finding of a failure to the forgiving assumption that the sensor is just broken, then the system's integrity becomes invalid. All the NSA or the Russians or the Chinese, or perpetrators of industrial espionage have to do crack into the 'enclave' is to spoof system integrity check into thinking a failure is just an innocuous broken sensor.
Likewise, the comments elsewhere in this thread that suggest there are legal requirements that Apple has to allow non-Apple components to be installed with impunity miss the implications on the system's integrity. To allow for the installation of non-Apple sensors, for instance, Apple would have to publicly share the security specs that would allow for non OEM parts to be inserted within the fingerprint 'enclave.' They might as well have the TouchID sensor automatically post every user's fingerprint data to this forum, because they really couldn't make the system any less secure.
You can argue about how forgiving or generous Apple should be to customers who find themselves looking at this error code, for whatever reason. O.K., fine. That said, arguments for any sort of relaxing of the security boundaries around the TouchID 'enclave' simply defy the logic of how such a thing works. It's either closed and secure, or it's not.