Also think about when peak demand happens -- late afternoon on hot summer days. Right at the time when people are getting home, with their EVs discharged (or at least, not at full capacity) after a day's use.
The grid is already perfectly capable of consumer feed-in, hence the huge deployment of photovoltaic solar systems. The metering is not particularly difficult. There is an emerging standard for smart grid communications (LTE on the 450MHz band) that is already in widespread use across the EU.
Completing this transition won't be cheap, but there are no significant roadblocks. We know what needs to be done and we have the technology to do it.
https://www.drive-electric.co.uk/driveelectric-launches-vehi...
http://www.energynetworks.org/assets/files/electricity/futur...
http://450alliance.org/wp-content/uploads/2014/05/WhitePaper...
Not completely discharged - the little available per car will add up to a lot when there are a lot of EVs. The EV owners who decide to sell to the grid at peak hours (at higher prices) might make a profit doing so.
Currently utilities buy power during peak times from other utilities, or fire up expensive peaker generators to manage the load.
A network of charging cars could be managed as another resource with a price attached to it that may be cheaper than the alternatives. I like the concept of varying the price of the charge based on your participation in the network.
At least in Florida, USA, most residential electric meters are flat-rate (same price per KWh, no matter what time of day you are using). A good portion of commercial meters have a peak and off-peak rate, as well as a single line item charge, based on peak demand, that is often 30-40% of the entire bill. The off-peak rate is often 50% or more cheaper than the peak rate.
Since most people would charge at night, it would probably make sense to have these residential services switched to a demand and time-of-day based meter, which would further reduce the cost of electricity. If someone spends a significant time at home, the charging car could buffer peak loads during the day to offset the additional draw of the nighttime charging.