When I was a lot younger, pretty much every washing machine (here in the UK) had both hot and cold fill. It went away for three reasons.

1. Machines got more water efficient.
2. Direct hot water from a combi gas boiler became the standard (replacing big jacketed tanks in most houses).
3. New detergents led to a campaign to encourage washing at 30°C rather than 40-60°C
   It's more cost effective to heat a small amount of water directly at100% efficiency in the machine than drawing cold water out of the pipework and either heating it then rest of the way directly or pouring it down the drain until it ran hot from the 80% efficient gas appliance.
   Interesting to hear it might be making a comeback. I can see the logic if there's a source of hot water from a heat pump, provided losses can be minimised.
   Personally I have PV so (weather permitting) electric is preferable to gas other than for space heating and bathing. That could change though. As it is, the heat pump drier, efficient as it is, still accounts for the majority of the energy used for laundry, even with the washer doing an extra spin cycle.