I think the electric car as dispatchable load holds the most promise. I don't know the physics of the batteries but I imagine that reducing the rate of charge of many car batteries would temporarily reduce demand without causing a charge / discharge cycle of the battery and would benefit the stability of the system in the short term if required

Edit: Also using car batteries as dispatchable load and not dispatchable generation simplifies the problem for utilities. They still have to deal with increased load but not drastic changes in power flows.