A lot of good points but the counter argument is that if we had had more two way connected cars on the network, the blackout may not have occurred in the first place. Remember it was caused by 2 major suppliers dropping off within a minute of each other. The second supplier only just took the system over the edge - if there had been sufficient connected battery backup, the grid could well have withstood the temporary overload. The problem they had was due to rate at which extra capacity could be spun up. Battery backup can be virtually instantaneous.
Re: domestic solar contributing to the problem, again this was because very few are fitted with battery backup. When demand increases you can't just ask God to wind up the brightness of the sun and clear away all the clouds. When more cars are electric there will be a much larger supply of cheap batteries to create PowerWalls or equivalent. The 8 year life of EV batteries only refers to their life in the car because you don't want to be stranded on the roadside as a result of decreased capacity. Old EV batteries still generally have about 80-85% capacity and make very good fixed backup systems.