Except that they won't because a) EV manufacturers won't allow it (Tesla doesn't), b) EV owners won't want to drain their EVs' batteries for others' benefit, c)

Except that they won't because a) EV manufacturers won't allow it (Tesla doesn't), b) EV owners won't want to drain their EVs' batteries for others' benefit, c) even if EV owners wanted to allow it, they wouldn't necessarily all have their EVs plugged in when needed.