hot water return
No home automation needed. Put a valve on a pressure-feed return. User turns on the valve to rotate the cold water in the pipe back to the heater, switches it over to the outflow tap when it's hot enough (user will know from experience how long that takes, after the first couple of days; or can probably feel the heat in the fixtures).
There's a bit of cost in running the pressure to cycle the cold water back, but it's less than the cost of continually cycling. You also come out ahead thermodynamically. Continuous circulation means you're always exposing the hottest water to the coldest environment, offering a steep slope for heat to escape.
Also design-in cost to have the valves, pressure system & return pipes from each hot water tap.
The low-tech equivalent: keep a bucket at each tap. Run the hot water tap into it until it's as hot as you want. Set bucket aside, make merry with hot water. Eventually carry the bucket back to the hot water tank, pour it in through some sort of manual valve. But: you lose more heat that way unless you have a slave to take the bucket back immediately; and heck, we know that modern humans are too lazy to do something like that...
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