Indeed it sounds like LK-99 specifically is not something we'd want used for power transmission lines. From a difficulty of manufacturing POV (aka cost), and from the nature of the material (more of a ceramic from what I hear?) but also because it's composed with lead.

At this point in civilization, we know better than to string lead stuff all over the place in unconstrained scenarios. Anything built with lead should not be ending up in areas where it will not be contained and maintained professionally,, and surely should not be going into the general consumer waste stream at all.

Seems like the most compelling applications will be in MRI machines, and then within power generation, specialized super computing, etc.

The thing is that LK-99 -if real, still a big if- opens a new materials science sub-field where we can expect significant improvements over LK-99. So even if LK-99 is not practical for some applications of superconductors, that wouldn't rule out development of new materials that are practical superconductors.