You're right that it's mainly a power time shifting scheme. But there's no fundamental reason that I can see that it should be much less efficient than on-deman

You're right that it's mainly a power time shifting scheme. But there's no fundamental reason that I can see that it should be much less efficient than on-demand cooling - you can always insulate the ice storage well, and air tends to be cooler at night, so your heat pumps should be somewhat more efficient at radiating heat into the air than during the day.