Not necessarily smart. Here (France), most water heaters can be controlled with an extra "pilot" wire, or closing a circuit. It has been common practice since m

Not necessarily smart. Here (France), most water heaters can be controlled with an extra "pilot" wire, or closing a circuit. It has been common practice since maybe the 60s to have multiple mettering rates, and a dry contact (relay) on the electricity meter to switch on/off some loads (mostly electric water heaters, though some electric space heaters can be connected as well). These days, rates can be more flexible thanks to "smart" meters (communicating via PLC). Just after the russian invasion of Ukraine, there were plans in place to open the dry contacts of customers outside of the scheduled hours in case the electricity grid needed to shed extra load. Thankfully this didn't end up being necessary. What I'm saying is that you don't really require smart end devices. Put the incentives in place (deep discounts) and the rest will follow. You probably need at least one smart device to control the others if a timer is not enough, and I think the electricity meter is a good fit for that role.