Introduced by Zenith shortly after WWII, the 'Radionic' cartridge promised a breakthrough in sound for the consumer: Tracking at lower weight, the cartridge had a nano-tech (for its day) 2MHz coil detuned by tiny metal modulated by stylus (diminished moving mass/mechanical load).

I heard one of these for the first time recently (pictured), the best I've ever heard a 78 record sound!

I think you've missed a word - "tiny metal (??)...."

Looking forward to pic.

"tiny metal (??)...."

Yeah, a tiny piece of metal, like brass I guess working like a 'tuning wand' to create FM?
Circuit has miniature 7-pin shielded triode oscillator that also demodulates (like quadrature detector?)
So no mechanical load unlike a magnetic cartridge which is really a dynamo loading needle.
Crystal, ceramic, strain-gauge types also load on stylus,
resulting in tonearm absorbing energy, reducing dynamics?

The Radionic sounds unlike a record, more like an original tape recording, very nice.

Later in 1950s Weathers FM cartridge appeared - said to track at 1-gram & extend to 30kc.
Lots of mystery, legends about this one as few have heard it. It is said radio stations were
clamoring to get them, but they soon ceased production.

Some say the Radionic was variable Q (creating AM signal? - explains easy demodulation)

I was just talking to someone about the Radionic pick-up and he was saying these were in Wurlitzer jukeboxes (late 40s to early 50s?) and were later replaced with a ceramic cartridge. So they would have made it to Australia in jukeboxes. He said they were 250kHz AM and they had to later add valve shielding as it made a nice AM transmitter where other people on the street could listen to your records on LW band!