There's definitely a vein of "smart grid" technology that is based around the utility shedding the customer's load for them, in a sort of fractional rolling brownout. I don't think we need to go there, and that most folks would be rightly pissed off at the imposition of such by their mammoth utility.
OTOH, I could see a Nest-style device which can read the day-ahead price and adjust for the customer based on their own preferences being perfectly acceptable.
Note that load shedding can include changing the temperature by a couple of degrees. So, not only can it be an opt-in or opt-out situation instead of being "imposed", it can be something that most folks would sleep right through.
There's no need to "impose" this. It provides economic value, so it can either be seen as a discount for opting in, or an extra charge for opting out. People already do this in a manual fashion with time-of-use rates.
OTOH, I could see a Nest-style device which can read the day-ahead price and adjust for the customer based on their own preferences being perfectly acceptable.