[NiHaoMike]

Those three wires are already brought into most homes. I do agree that the application potential is limited as it has to be a device that needs a 240V circuit but internally does better with about 170V DC. Some apartments use 120/208V (with two phases accessible to a unit) and that will cause compatibility issues. One possible application is a variable speed condensing unit with a relay to select between bridge rectifier and full wave mode, boosting efficiency at low speeds. If it detects that it's actually connected to 120/208, it will just stay in bridge rectifier mode.

The harmonics cancel out inside the transformer, assuming there's a PFC stage.

The idea of using "HVDC" for residential power distribution is really about new construction, not retrofitting. It is mostly of interest in off grid homes, not so much on grid.