More and more of the new appliances these day (especially air conditioners) are able to be remotely controlled / throttled by the utility to prevent overloads.
The question is by who? If the power company isn't careful and routes those controls over a public network that they do not fully control then all bets are off regarding who controls the system.
By the time these new smart systems become deployed on a large scale i expect most appliances will have this ability.
I'm thinking you haven't worked too closely with a power company lately. The grid is positively archaic and certainly doesn't have the fine grained control you seem to think it does. The power company around me actively resists investing in upgrading their service faster than a pace that you could describe as glacial. They also seriously do not give a shit about their customers because they don't have to. Where else are they going to go?
In the last 24 months I have power company employees damage my property, start a fire (no joke), kill some wildlife, trespass, and cut down trees they had no right to cut down and cause enough trouble that our township supervisor (our version of a mayor) actually came on site to find out what the problem was. And I'm supposed to believe these people will have the competence and diligence to worry about some clever hacker turning on my AC? Yeah, I doubt it.