Hot water pipes are not necessary with tankless hot water systems at points of use.
Inexpensive consumer hot water showers can be adapted to provide water for both a bathroom shower and faucet, but I think they don't have the capacity to vary the wattage applied based on water flow rate.
For a constant wattage, if someone increases the flow rate by using the bathroom sink while the shower is being used, the water temperature arriving at the shower would drop.
A constant wattage to flow rate ratio would only be important where one heater supplies more than one faucet or shower.
Perhaps for simplicity and cheaper hardware, each point of use would have it's own heater.
One downside to tankless hot water heaters is their high power demand. They require expensive thicker gauge wire. Typically the cheap shower heaters I've seen have a maximum setting of 6000 Watts. A shower with a spa quality flow rate requires 10,000 Watts.
For an off-grid home, can the power demand be harmful to the energy storage batteries?