Yes smart applicances could be told to start and stop based on grid conditions, but its tricky to start and stop your washing machine in mid cycle, that can work but its shifting demand rather than consuming over-supply.
Plus there is the problem that a smart appliance needs a smart grid to talk to, and to have a smart grid you need a smart government ;)
It does need joined-up-thinking, but some types of devices do not need constant full power, e.g. anything that is charging. To improve the world we need a mix of better technology and changing attitudes