If this LK-99 stuff is real, it would allow (potentially) for lossless electric transmission lines at great distances; mainstreaming of efficient nuclear fusion; anti-gravity cars or plane...
and so much more. The possibilities are almost endless.
We are still not sure. The paper was published under very suspicious circumstances. However, since the recipe is given in the paper, many groups around the world are running tests. We still need to wait a few more days for more conclusive results. With the results until now, it seems that the material is at least very strongly diamagnetic but I haven't seen any conclusive proof of zero resistivity confirmed by another lab.