I think EV owners would need to find some level of compensation for the additional cycles they would incur. Electric vehicles are expensive because of the battery so deteriorating the life of one of the most costly parts of the car doesn't feel like a great solution.
I also wouldn't want the battery level timed around the grid vs my own transportation needs. What if there is suddenly a heavy demand on the grid, and now I can't take my sick family member to the hospital, because the charge was sold to the grid?