Depends on how much energy gets lost in terms of heat during the charging process. If they can get better efficiency during the charging process(less loss due to less heat) with these batteries then perhaps this would help mitigate stresses on the electric grid! Brute force charging might be a real stressor but if there is an option for a gentler but longer charging period with these batteries...say and hour or two, then the electric grids might not be in such danger.
One needs to look at the average usage.
At 12k miles per year, that is 33 m/day or about 8 kwhrs.
That is about equivalent to a central AC running two hours a day.