Sure, fast charging will add some day-time demand, but it's not much. Cheap night-time pricing keeps the charging demand off-peak.
More even demand curves make generation more economical. It becomes trivial to upgrade distribution where needed.
https://www.eia.gov/todayinenergy/detail.php?id=830
During "peak" hours they're using roughly 17Gw total, and during off-peak, it's at 15Gw so we've only got 2Gw total to buffer electric cars charging.
Feel free to tell me how my math is wrong, but let's assume worst case scenario: a tesla charger lists 11.5kW max draw. There are roughly 14m people in New England, if we assume even half of them were charging overnight, that's 86Gw of power draw. Even if you back that off to 25% of the population and half the power draw from the charger, you're at 21.5Gw of power, which is 10x what is available, and more than the total power usage during peak hours.
If someone else has some different math I'm all ears but I don't know how we're going to more than double the total power capacity in 10 years - even if you assume we can get there with renewables, the backend infrastructure can't handle it.
The average household uses <1200kWh per month. Adding another 18kW per day increases power usage by almost 50%, which goes back to: the national power grid doesn't have anywhere near 50% spare capacity.
I would be surprised if even half a percent of Americans have that kind of setup. If even 50% of Americans suddenly had that setup and all gamed every night for 10 hours a night, I would expect that would also cause the power grid to have issues.
The peak power draw will lie somewhere between your estimate (11.5kW/vehicle) and the typical estimate (920W), which would assume everyone charging at home. Clearly not everyone would charge at home (or with a 1kW charger), so the number is in between.
Both transmission and generation tend to cost mostly their peak usage. Generation is likely easier to upgrade, given a few years. I would imagine transmission is significantly more costly and complex, since the last mile network is enormous, but transmission likely has much more overhead (it has a soft instead of hard maximum as well due to simply increasing losses and increased thermal stress). I would say we probably are nearly prepared (with significant generation investments) if everyone charges at home at low power -- a 1-2 decade transition would go smoothly (my guess/estimate is 65% more average usage by that date). If most people opt for fast charging, the system will need significant overhaul (with widespread use of buffer batteries helping). It seems very wise for State incentives to increase capacity as soon as possible, to anticipate market demand -- the energy sector is likely slower than the automotive industry.
Except the people that don't have a charging station in their garage or folks that have a power outage. Just this week, we had a heat wave (70-80F) and winds up to 90MPH across California that resulted in power outages throughout the state as well as several fires.