I think this is a practical limit as far as conventional conductors go. Unless the superconductors are ridiculously cost-effective to install and maintain, the benefits will never materialize - i.e. become a game changer.
To put this into perspective, let's try this. A relatively small country like South Korea still has more than ten thousand miles of transmission lines. Say you replace all that and achieve 4% more power.
Since the installed power capacity is around 70GW, that means about 3GW, or about three regular nuclear plants. I highly doubt completely redoing the existing transmission infrastructure with conventional means is possible with the cost of building three nuclear plants, let alone a superconducting one. And I haven't even got to the current limits yet.
This is why, if there's a superconductor breakthrough, I think it'll have more impact on medical uses rather than raw power transmission.
Disclaimer: I work in the electric power industry.