When that day arrives, ICE autos will probably become very affordable.
History might not repeat itself. But I would be unsurprised by a greening policy for electric vehicles that looked a lot like cash for clunkers. The long run of tax favored policies for electric vehicles don't suggest future policies designed for the means of those without means: there never has been a tax incentive for buying a used electric vehicle or replacing a vehicle with low fuel mileage for a more efficient used vehicle.
Trickle down theories tend to ignore the incentives for those at the top of the hill to capture any value that might flow downstream. Cash for clunkers didn't buy used cars from poor people with a yard full of junkers. Because of the holding period required, they weren't salable on their potential trade-in value to people with the means to buy new cars.
Never mind that part of transportation greening is raising the price of gasoline.