24V is okay. 48V would be nicer for indoor use.
Also low voltage wiring can legally be done by anyone in NZ (a bonus when doing your own work, and a pitfall when buying a house?)
Other circuits must be 20A, e.g., kitchen outlets serving appliances.
A summary of standards here: <https://www.thespruce.com/common-electrical-codes-by-room-11...>
A 15A lighting circuit can serve up to 14 100W bulbs. Or 150 LEDs drawing 10W each....
And besides, idk if you have ever pulled 12ga wire, but it's a pita. Idk any electrician that would agree with you saying it would be a pain to cut back on heavy wire and pull half that with light 22 awg.
Not extremely thick. Wire losses remain similar at 12V as they were at 110V (Replace 100W bulb with a 10W bulb at 12V, current remains ~1A so wire losses stay the same as the were). Wire losses might be say 1W for 1mm2 cabling.
Agree that it is worth upping voltage to chase a few more percent savings, but still need to consider other constraints.
Heck, with such a standard you could have 120VAC -> 48VDC converters and you'd be in the same position we are today with Leads, only better because you'd just have to replace the converter and not the whole bulb.
https://www.sansiled.com/blogs/learn/what-are-the-benefits-o...
<https://www.designboom.com/technology/self-cooling-100-watt-...>
<https://i.pinimg.com/originals/b5/c2/c5/b5c2c5d69fb240a571ba...>
It's also helpful to recognise that existing lighting fixtures and lamps were designed around the constraints of incandescent bulbs. The first generation of LED bulbs and lamps largely conform to these. As LEDs mature, both fixtures and lamps which address the limitations and requirements of the technology (transformers, perhaps dedicated 12v circuits, heat dissipation for the transformer rather than lighting elements themselves, and better light-temperature and intensity regulation) should emerge.
We're presently in the somewhat-messy half-emerged state. Think horseless carriages, wireless, and the days of dual gas/electric lighting and lamping systems (yes, these existed, and yes, the failure modes were ... much as you might imagine).