With the prevalence of "planned unit development" style suburban housing design I've always been a little amazed that no AHJs require district heating/cooling solutions. Here in Texas they already require PUD-based water and wastewater so often the first developments in rural expansion of the cities have their own small water and wastewater treatment systems.

Its a small step to run hot/cold water supply lines when you are using tax-free muni bonds to put in the streets and sewers already, and have to have a maintenance fee structure that operates the plant.