> at basically no cost for the EV owner?

Only if you have a battery with unlimited charge cycles. This doesn't seem possible with current technology - and even if it were, manufacturers would still optimize for higher density and reasonable longevity after 100,000 miles. Most people would average a charging cycle a week, so they can't see the difference between a 2000 cycles battery and a 50,000 cycles one in the life of the car, but they can definitely feel the effects of range anxiety.

When you do daily or multiple times a day cycles, as is typical for grid applications, that's a completely different beast, for example a shallow charge cycle at 70% which increases the life 5x is much more profitable because it reduces overall battery replacement costs.

And when you factor in the much higher costs per Wh for car batteries, which are custom spare parts not mass produced commodity cells, you will find that the cost you incur in vehicle depreciation far exceeds the value you could earn from intra-day energy market speculation.

The idea is you wait to charge until prices drop, rather than charge as soon as possible which adds zero charge cycles or degradation. Discharging into the grid is unlikely to ever be profitable for the average consumer but it isn’t impossible for the economics to work out just look at how high Texes Grid prices have gotten during extreme events.

Delayed charging is already a common feature on many EV and could shift demand quite a bit in aggregate.

Also, battery degradation reduces range so there is an impetus to extend useful life well past expedited useable life. Aka if you want 95+% capacity at 100,000 miles that’s inherently increasing capacity at 1 million+ miles. Manufactures do care about resale value so useful capacity at 100k miles is likely to improve over time.

There is some talk about virtual energy providers that could agregate a large number of home users, receive an availability fee and only physically discharge during emergencies; that could work out economically and allow owners a positive revenue after depreciation, that could translate, for example, in lower prices for energy. That being said, I still think the whole fixed costs of the scheme (smart bidirectional meters, EV and charger support, coordination and administration costs etc.) would make it a money-losing proposal. A nice idea in theory, like say IP multicasting, but that cannot be made to work effectively in the real world.

The benefits of delayed charging are limited by the electric consumption of the transport sector. For an average family driving no more than 800 miles/month at 4 miles/kWh it works out less than 200kWh/month. If half of that charge is time flexible (with the rest being achieved at fastchargers or when the owner is in a hurry etc.), you get a 100 kWh/month dynamic load, a sizeable yet small fraction of the total household consumption. I would earmark that under smart-grid approaches, if correct pricing incentives are set at the meter it will happen automatically and not just for the EV charging loads.

A family only driving 800 miles a month is very low. The average driver is over 12k miles per year and 2 car families are extremely common.

Also, a relatively low percentage of charging is vis fast charging. Even a normal wall outlet can provide enough power do drive 15,000+ miles a year assuming normal habits, and level 2 home chargers are common.