And if that malware can't liberate USB access, and still needs to read data (rather than just writing it), it could exploit the capacity for various devices to

And if that malware can't liberate USB access, and still needs to read data (rather than just writing it), it could exploit the capacity for various devices to emit detectable EM radiation. The fake keyboard/mouse, being inside the Faraday cage, would be able to sense that radiation and extract data that the malware in its payload sends back to it. In fact, all of this would work equally well with a PS/2 port.