I’m not an expert on this, but I think superconducting wires have an current limit, as a current flowing creates a magnetic field which the superconductor has to repel. I read that the paper states a very low current limit for LK-99, meaning it loses superconductivity once a very modest amount of current is passed through it.
It's hard to tell what the critical current density of LK-99 is, because their sample is porous and probably very impure. They measured the critical current they could pass through a sample, but the conducting cross-section is somewhat unknown. Its high critical temperature suggests that it should probably have a higher current capacity than other superconductors. That said, in the extremes, current density is also limited by tensile strength, because electromagnetic coils repel themselves.
I believe the implication is that LK-99 is basically a demonstration of an entire class of materials which should have room-temp superconduction properties. IE we can enumerate through the entire class and find the ones with the properties we want.
A limitation...at ambient temperature and pressure.
Usually this is an optimization frontier, where something that has tetchy critical current/field at high temperature is going to have very good critical current/field at the same temperature as a lower-Tc superconductor.
If it superconducts at all at room temp, cooling it down even to 200K (about dry ice temp - quite cheap to do) could get you something very usable.
