A material with no electrical resistance. Build a wire out of it and the voltage will be the same on both ends.
Great for energy transmission (though you can't put too much current, superconductivity breaks down under strong fields).
Great for fast circuits, such as CPUs, that don't waste energy just transmitting data.
Great for storing energy (in principle) by just making a loop and let current flow indefinitely.
Related, great for building powerful magnets (that are just such a loop) without wasting too much energy. Applications: MRI machines (they already use superconductors but are bulky due to the need for cooling) and other powerful magnets: LHC/particle accelerators, Tokamaks/plasma control/fusion. But also improved motors and generators.
Nice for levitating stuff since they levitate above magnets "for free" (due to their interaction with electrical fields, they reject magnetic fields). Possible applications for maglev (trains, etc), magnetic bearings, etc.
And possibly a lot of new applications opened up if you remove the need for cooling (Faraday cages?).
Of course, it all depends on how much current and temperature it can handle. But if this is real, just having one material is game-changing, and it will surely be improved upon by looking for similar properties in other materials. This one contains lead, which is a non-starter for a lot of applications due to its toxicity.
Someone else wrote a few use-cases in that other comment: https://news.ycombinator.com/item?id=36866686
We've been using cadmium-based batteries for ages despite Cadmium being even more toxic than lead, and are still using lead batteries in ICE cars AFAIK. Lead toxicity isn't really a problem unless you burn it, deliver water through it or you put it on paint that end up in kids' mouth…
Lead batteries for cars are a bit special, as the whole supply chain goes both ways for recycling, while batteries are rather self-contained and not usually exposed to harsh environments.
Though I suspect you are right in the end, as it's a matter of judging the risk vs reward, I wouldn't be surprised if other materials with a similar structure end up performing similarly.
Pb is also quite hard to use in integrated circuits, as far as I know. I am no material scientist, but it could be due to its low melting point or tendency to contaminate other metals.
The definition of an insulator is a material that holds (up to some amount of) voltage without electrical currents appearing.
Your example needs two wires. And the wires themselves don't have any voltage. All of the voltage is between them, and is only there because they are insulated from each other.
You are conflating 'insulated' and 'insulator'.