The person to talk to is @steve, this is his area of expertise.
Most homes aren’t wired for the instant yet but getting there. Heat loss is a major issue and where I have recirculating hot water, I’ve dealt with and spent a lot of time researching in my design and installion of the system.
If I had to do it again I would use a heat pump water heater with auxiliary heat. The power factor on those is unbelievable at over 3 to 1