Unfortunately for coal, not all of its problems are externalities as much as they used to be. If your customer is paying for it, even if not directly in the price you charge, that can alter their behaviour, as we are seeing around the world.
To the extent that customers actually change their behavior, that is a positive development. I'm not sure the effect size is particularly large.
Efficiency programs have been pretty successful, and the overall trend in power consumption (in the US) is negative for now, which is great. But relatively few people even know what fuels are used to supply their power, so I'm not sure how easily consumers can respond.