Re: Off peak?
To elaborate a little more, the user could select a priority level. In effect, a frequency-monitoring charger could be set to shed load on line frequency drop if the user was relaxed about getting more charge, or to remain connected (at extra cost) if the user urgently needed it. There would have to be something like this, as a lot of extra load switching in and out at exactly the same frequency point would do nothing for system stability.
Also, a freezer that has been shut off for a while gradually becomes a higher priority, but I guess that need could also be built in at relatively low cost per unit.
Who needs smart meters? Just charge consumption according to the prevailing line frequency ... though it would be necessary to ensure that the system wasn't run at an artificially low frequency to produce increased revenue! Now, how to do that?