Bi-directional power flow is already embedded in every EV. Accelerate -> energy flows from battery to the electric motor and brake -> energy is flowing back to the battery. When the EV is charged from a charger the energy is flowing into the battery so why could it not also flow from the battery to the charger? You may say that this would be expensive for the OEMs to implement such a solution, but this is definitively not true. Nissan (and most EV OEMs in Japan) have shown that bi-directionality can be implemented cheaply in low cost EVs.
Consider the value of V2G versus V1G (charging only):
1. Frequency Regulation in Denmark has shown that the value of V2G is 7 – 13 times the value of V1G (Thingvad, Christensen 2016)
2. Discharging 10 kWh @peak hours/day in California V2G can save the user ~ $1,100 per year i.e. $8,800 over the lifetime vs V1G can only time shift charging
3. Lastly V2G can provide energy resilience in case of wildfires, PSPS events or natural disasters
History has shown that such a big value differentials will be challenged by market forces and lead to more and more EV OEMs implementing bi-directionality since it offers superior value to their customers (earnings, savings and energy security)