Good Lord, you actually believe this?! This is a very old concept going back to the start of giant scale gassers during a period when magnetos were just about the only type of ignition to be had. Mostly prior to the use of carbon fiber for anything that was non military.

I fly aircraft that are constructed almost entirely carbon fiber. There is zero metal or wood anywhere in the structural components. One of the few pieces of moving metal in the things are the metal throttle linkage rods with plastic housed ball links at each end. Gas engines and electronic ignitions. At 100K a copy do you really think the RFI issue has not been fully and completely researched? BTW, the only "ground plane" is at antenna locations so let's rule out RFI elimination via grounding other that at the plug wire. Oh, yea, resistor plugs as well. BTW, this is the second type of brutally expensive aircraft that I have worked with that used a similar linkage arrangement.

On all my personal stuff I use only a metal or C/F rod with similar ball links at each end for two reasons. #1 is because it's rigid. #2 is because there is no RFI transmitted back through the rod. For something to transmit it must first be physically connected to something else that radiates. The C/F rod is not connected to anything electrically. Test the same type of installation with a continuity probe and tell us what you get.

Bottom line is that if properly connected with what amounts to an electrical isolater at each end it doesn't matter what you use for a throttle linkage rod.

However, that does not eliminate the possibility of interference caused by vibration induced electrical noise generated by physical contact with other metal components. As in any other component, a little care needs to be exercised by the builder to eliminate any metal to metal vibration anywhere on the aircraft.

Pat