Beautiful design. Curious since you mention the issues with plastic, what's the part that you couldn't avoid plastic for the trefolo (given you mention it's 0.01% plastic)?
About the only kind of fully plastic-free cable I know of (other then historical examples) is bare MICC aka "pyro", which are copper tube sheaths filled with magnesium oxide powder and the wires in the middle. It's used especially in fireproof installations.
A huge pain to install as it's so stiff and needs special tools and fittings to keep it from absorbing water from the air. It has a large bend radius, and it only good for fixed installation as it will crack open if you bend it a few times. And it's nearly £1000 for 100m. So it's not very popular these days.
Plastic really is an annoyingly wonderous category of material when you consider the flexibility, insulation, mechanical, thermal and chemical resistance it can have (and the price)!
Electric cables are made from insulation (plastic) and wires (metal). Wires use metal, insulation typically does not, so it's NOT easy to make a whole cable out of metal.