On the ‘would someone make’ front..
I’d like to see the math done as to how much energy could be saved by a heat pump water heater that had a tank for the greywater coming from the shower/bath. The idea is it could use a normal air exchange when no hot water was available that had returned from the bath, but it could extract the heat from the hot water coming back from the shower/bath if there was any. It seems like this ought to lead to considerable energy savings for a tanked heat pump hot water heater in normal usage since it would be pumping only slightly uphill. One can envision a system where the heat exchanger wrapped around a pipe leaving a insulated tank and a valve opened to empty the cold water and fill with more hot whenever the water had been pumped down to ambient.