I can readily imagine some cross-discipline techniques achieving this. A little lithography, some selective dissolution like Gorilla glass, perhaps some tricks from the optical fiber industry, and bam, you have a fine coaxial filament which creates a region of 100's-of -MPa stress along the length of the fiber. Maybe even GPa, though that's tensile-strength-of-nanotubes territory.
Certainly it's years away but I dunno...This feels possible in an engineering sense.
>100's-of -MPa stress along the length of the fiber
It's all fine and dandy until it breaks open, along the length, and releases not just the stored mechanical energy, but also all the inductive energy from the flowing current of few million amperes.
Superconductors aren't magic. You can't just stuff a few million amps into a tiny wire. Just as there is a critical temperature, there's also a critical current density. While those two numbers are related, you'll need quite a bit more than "room temperature" superconductors to carry currents like that. And there's a temperature/current tradeoff: if the ambient temperature is close to the critical temperature, then a whisp of current can make it go normal.
1 meter of 1mm diameter wire with 1 million amperes amounts to 750kJ, or ~180g of TNT.
A superconductor blowing up across the length and distributing the energy doesn't seem as bad a whole transmission line's energy released at a point fault.
Assuming superconductors replace existing wires, it won't be more power than the wires already carry, just in a smaller area.
My instincts tell me it would actually be much safer. Overheating wire would instantly lose superconductivity and vaporize into an open circuit. The same thing a fuse does.
Current wires have enough bulk to heat up and melt slowly. This is more opportunity to burn things and set stuff on fire. Vaporized plasma is low density which probably won't concentrate energy enough to light surrounding materials on fire. Plasma also disassociates quickly in air, again way less time for fires.
For mechanical stress, it may be sufficient to just ensure the stress is evenly distributed in all directions. This way the energy will be driven into shockwave and heat rather than motion. The wires might make a big bang but this isn't very harmful underground or high in the air on lines. Explosions are way less dangerous in open air than they are confined
Put two superconducting fibers next to each other with a thin insulating layer, or many fibers in a bundle.
Have the supercurrent in one direction matched by the same supercurrent in the other direction, alternations as closely spaced as possible.
The magnetic field will be confined, at least.
When the fiber breaks, join the entwined superconductors together (equivalently: have the insulator break down), and the current in the rest of the transmission line can continue flowing.
Certainly it's years away but I dunno...This feels possible in an engineering sense.