The reason people are trying to get carbon nanotube electricity lines in the air is not because 'nano' is a cool word, but because they're really light while conducting electricity. Lead is, well, quite the opposite of that.
Buried cables used to be lead jacketed before viable polymers suitable for long term use were developed in the modern era.
There are significant problems with swcnts (and even more so with dwcnts or mwcnts, due to less effective macrophage breakdown from h2o2 release). But there are some applications where their use can be a large improvement. The fact that only very well trained professionals should ever come in contact with certain materials (like extremely high powered lines) makes this use case more acceptable. Additionally, concealing swcnts in a polymer and using extrusion methods of chlorosulfonic acid into carbon tetrachloride to make really compact nanowires can help quite a bit for making the product affect the public less if any problem may occur that downs the power lines.