This is beyond a huge stretch but your creativity is appreciated.
Building a network tap into a CAT5 cable isn’t that hard you just need to essentially modulate the traffic into RF and have another implant near by that can intercept the radio signals.
We live in a day where we have demonstratable side channels attacks against RSA keys by listening to how a laptop squeeks when it’s under load and you think building a chip into a cable is a stretch?
Heck I have one cable like that atm which is a converter from a model M keyboard to a USB you can’t see the converter IC it’s built into the RJ45 connector the keyboard originally used without any additional bulk.
I’ve seen a demonstration of similar taps on VGA cables that transmit the entire image to a remove reciecer which is often implanted near by in a power socket, light fixture or anything else where you have a reliable power supply and enough wires to hide and even transmit a signal out side over the power lines.