You don't need a chip for this. And to their credit Librem laptops have offered such a hardware switch for a while now (perhaps since they began selling laptops) with (as I understand it) no chipset involved.

Putting this functionality into a computer chip is ridiculous and unnecessary partially because there's no clear way for ordinary non-technical users to control that, and partially because this suggests that software (as I presume the software on this new chip will be alterable by Apple) can still affect whether the mic is hot. The headline "Apple's T2 chip will prevent hackers from eavesdropping on your microphone" should probably be interpreted to mean that Apple won't be prevented from listening in.

Camera access and wireless network access should also be physically disconnectable via a simple user-controlled piece of hardware which electrically disconnecting the on-board webcam and wireless network device from the rest of the system -- a slider or rocker switch. This too is something I understand Librem laptops offer but is uncommon elsewhere.