Low-voltage DC needs 10x more copper for the same power, and extending power runs to "home run" makes the wires even longer. Unless you pay for that extra copper, wiring losses will eat your savings. The big issue with ACDC conversion is that the AC is 60/50 Hz, which means energy storage of 8-10ms x wattage for efficient conversion is required. Better efficiency and lower wiring costs would come from using higher voltage DC and/or higher frequency AC. Aviation, submarines, spacecraft, trains and some industrial tools use 400 Hz AC - which allows for smaller transformers and motors. DCDC converters essentially have internal oscillators to perform the voltage conversion, and can choose an even higher frequency to minimize energy storage time. The reason we're still using 60/50 Hz is because it's the way things always were, just like train gauges are a good match to two horses side-to-side, and perhaps because 60/50Hz hum is less annoying than 400Hz hum - but hum just means that you're losing power to the environment, so it's power efficient to eliminate that anyway.
That being said, when retrofitting incandescent lighting systems with lower-power lighting, it could make sense to use existing wiring at a lower voltage AND LOWER POWER LEVEL. That way the power/voltage conversion could be grouped together in one or a few places so that higher-efficiency converters can be used, but still kept close to the points of use to minimize wiring loss. Unfortunately, the retrofit market is going for power conversion in individual lighting fixtures so one fixture at a time can be changed out.