It is a very large assumption that the packs found in all cars will be the choice of utility companies. Electric car manufacturers (full EV or PHEV) cannot even agree on chargers.
To me this idea that utility companies step up is like the age old promise, the check is in the mail. Until a full life cycle plan is shown and incorporated as part of each sale its simply a sales gimmick.
Plus we haven't hit the tip of the iceberg when it comes to new regulations governing these cars. They are new and they are very PC now but laws will come along to deal with them, the first being, how do you tax them since they won't be caught at the pump? Politicians won't let that go easily. Plus we haven't seen how response crews will handle these cars in accidents. Testing is one thing but people tend to wreck cars very differently from how tests are performed.
There is also the incredible cascade effect of electric only cars. (disclosure I work for a major parts distributor) The majority of what automotive stores sell and repair shops fix simply don't exist in these cars. How many years before battery technology pushes more than your corner fuel store out? Jay Leno on his Jay Leno's Garage series recently remarked on how little his nearly hundred year old electric car needs. This will be true for the current and new generations.
Still back to your point, until I see it regulated or guaranteed in contract I don't subscribe to the idea the utilities will step up. There will vastly easier solutions for them, like taking up all those batteries that end up in government vehicles from fleets of buses to cars.
