it could put a call out to any EV currently plugged in saying "I'll pay 6 cents per kWh for what's in your battery". If they don't get as much power as they need, they would put out another request at 7 cents. If you paid 4 cents the previous night, that's a good deal for everyone.
You'd be an idiot to accept that deal!
1) Your EV's battery doesn't charge/discharge at anywhere near 100% efficiency.
2) Batteries have a fixed number of charge/discharge cycles, so the energy you pull out is significantly more expensive than the electric rates. It may not be much cheaper than running a gasoline/electric generator in your back yard...
3) On a TIMEÂ-OFÂ-US rate schedule, you pay about SIX TIMES HIGHER for your daytime electrical usage. I just found Nevada Electric TOU summer rates of $0.06159 for off-peak, and $0.36554 for peak (all-day, really). So until they're paying you more than $0.40, you'd be far better off serving your own household's electric needs from your EV's battery, not selling it back to the grid. Of course nobody does that because of point #2 above.
4) If it was at all a profitable proposition, the power company would cut-out the customer, distribution losses, retail rates, etc., and build their own battery banks. That they don't should be a huge hint that the economics don't work.
5) As an added bonus, your car doesn't have its full range when you suddenly need it, and it will take an hour to top-off the charge.
6) If utilities would quick trying to heavily penalize residential PV customers, they would quickly get lots of Summer peak power.