What do you think 12V would solve for lighting? Are LEDs going to magically run cooler if the driver is fed by 12V instead of 120V? My house is almost entirely LED since I changed it out in 2011-2013 and I think I have had 3 bulbs fail in that time, all of which were in enclosed fixtures, I have since found some bulbs that don't seem to mind that. Nobody in their right mind with any understanding of EE would contemplate wiring a house for 12V. Try living in an RV or boat for a while and you'll quickly realize what a hassle it is to be stuck with such a low voltage. A 2V sag under load is no problem for 120V but it's completely unacceptable for 12V.
Not 12v but 24v or 48v.
Much simpler circuit inside the bulb: you won't have bridge rectifier, no bulky fuse, no common mode chokes for filtering, no primary high voltage capacitor, no need for transformers with double insulated wires or with space between primary and secondary, no cutouts in pcb under transformer ... a simpler and cheaper inductor instead of bigger transformers...
Better factor correction, you can have a 120-230v -> 24/48v that's 90%+ efficient, with 95+ factor correction instead of separate ac-dc converters in each bulb with 70-90 pfc.
Most led bulbs use small leds, let's say up to 100mA ... so 24v or 48v would be fine for having multiple leds in series, even if using cheapest linear led driver, losses would be very small. ex have 7 x 3v 0.1A in series, then 2-3 of these in parallel for 21v 0.3a ... you get 7.2w in, 6.3w out .. 88% efficiency with cheapest linear led driver out there.
Cheaper bulbs, or maybe better heatsinked leds for longer life, as the led driver inside may be more efficient and generate less heat.
much easier to produce 3.3v or 5v for an integrated IC that could do dimming based on signals on the DC input line or from bluetooth / wireless signal.
Less waste that won't be recycled properly...