Or small! :D
Transmission lines are a great example of competing demands. Copper is a better conductor so why do we use aluminium? Because of weight. And weight is a huge factor in supporting large cables over long distances.
Metals are also ductile, which is important for a cable to hang in gravity under its own weight, be moved by the wind and so on. Assumedly exotic crystals wouldn't have this property. Even if they could, what would the weight be? Would the cross-section need to be much larger? Particular to this family of superconductors, tungsten isn't exactly the easiest thing to do deal with, particularly on a massive scale.
There's an interesting Reddit thread about this topic [1]. One issue it raises is we'd need to essentiaally rebuild our entire infrastructure and transformers are a big part of that.
Personally, I think energy is going to get an awful lot more local. Solar is our future (IMHO). The ability to store excess power generated during the day and then use it when it's dark or cloudy will obviate the need to expensive long-line transmission infrasturcture from distant power plants.
Lastly, the GP is correct: liquid nitrogen is incredibly cheap. It's basically the cost of drinking water. Getting something we could use at liquid nitrogen cooling temperatures would be incredibly impactful.
[1]: https://www.reddit.com/r/AskPhysics/comments/12etlkr/wouldnt...
https://www.caiso.com/documents/2023-special-report-on-batte...
The voltage can be substantially lowered, because high currents don't lead to high losses; the current may be made as high as practical, near to the limit of the material's superconducting state.
Hold on, what? How?? Reaching that temperature seems like a difficult task; and what's used as a source of pure nitrogen, anyway? Is there some clever trick to separating it out from the air?