I’m a lot more skeptical of a CME or solar flare causing the kind of geomagnetic currents to take the whole grid down. We learned a lot from the 1993 blackout. Also, we have satellites around the Sun that can send us warning at the speed of light, a lot faster than any solar mass ejection would travel. In the worst case— a super-Carrington event—the grid can be shut down and saved.
I have always thought that each state should place an AC-DC-AC trip/trigger at their borders on any power lines that cross state boundaries. In the event of any kind of EMP, it would significantly limit the “travel” of the pulse waive. And having worked on the networks at the western national grid, I beleive we do not have enough segmentation in place.