I think it's pretty common to have time-of-use pricing (that's what my provider calls it, and I am on the plan), but it's relatively fixed. Ours switches schedule twice a year. So you can get used to it, I only charge our EVs after 10pm for example. But if it changed dynamically, I'd need to have a lot of automation in place to react, because it would get tiring to personally pay attention to price all the time.

>Some states have this. I remember a friend in new york had a timer on his electric water heater to heat it at night when power was cheap.

This has been a thing in Australia too, under the decades-old assumption that midnight coal is the cheapest period of power. There have been projects to change the boiler systems to 1) heat at midday instead of midnight, to reflect the changed cost-curve caused by solar, and 2) randomise the exact period of heating, to spread the demand over a range rather than causing a huge spike at 12:00 exactly.