No matter what (if anything) replaces coal for electricity generation, it's going to take some time to switch to that new source. If, at the same time, we also start powering cars with electricity, the conversion to clean power might take even longer.

Clean power might cost more than coal power, at least initially. So plug-in cars might provide a stronger economic incentive to keep using coal, since people just love cheap transportation.

I'd really rather see electricity used for buses (and/or streetcars) and light rail, as these are inherently more efficient than private cars of any type.