For this to actually happen, it’s going to require a major drop in the cost of nuclear power. To some extent, pushing nothing-but-nuclear has been a fossil fuel industry strategy because those high costs and long lead times mean that it’s not actually getting built.
The point was more that days with half as much wind and solar as the average are extremely rarer. It is a bad day when it is at 60% of the average. So you really need something like 50% overproduction and maybe a days worth of storage with such a grid. There are also other forms of electricity production like hydro, biomass, waste burning and geothermal, which are either baseload or dispatchable by nature. Also losses for high voltage power lines are something like 6.7%/1000km for AC lines. That is not that horrible either.