I think there are many points here that are not understood.
1. How is the Motherboard going to step down the Voltage, are they going to choose and inefficent method of using voltage dividers, this would make the space better, but you will have immediate losses on the use of Resistors. Otherwise the motherboards are all of a sudden going to have to house some transformers, which are going to spew Electromagnetic interference all ove the Motherboard and surrounding components. Or are they planning to try to dephase the voltage to try to split the voltage up. This could spell disaster, as they already split phases within the regulator section to power the complex out of phase circuitry.
2. 3.3v is the threshold of voltage efficiency loss benchmark. Voltages around and under 3.3v suffer from less loss due to electromagnetic induction caused in all wires as a response to current passing.
3. The Motherboard is going to have to have more thermal protection as the average voltages speeding around the system are going to be higher, until they hit the transformer that is going to drop the Voltages to 3.3v
4. As technology shrinks the Transistor size, the voltages required to switch the FET's can be designed to drop requiring the voltage to be less, and the current to be more, but the power envelope still remains the same, or distributing more 3.3v pins to the board so that it works like a signal extender to make voltage shrinking tech more viable.
5. The 12 volts were mostly needed for the HDD that used to have spinning platters. Other uses are within some of the sub systems, but if all are designed to use less voltage now, it may increase the wireing, but it will decrease the size.
6. Phones are a typical example of power from a 5v only range. They drive similar tech with far less requirements that the desktop equivalents.
7. People need to stop asking for over drive tech, were the power envelope is pushed to achive performance. It is diminishing gains, and phone tech is a proof that, if we are more patient, we can have 70% less performance, but massive increases in efficiency, in a world obsessed with CO2.
This move from Intel makes no sense in light of the CO2 reduction mindset. It just proves that the owners are all mouth about the "green new deal" and no action, because people just dont understand the connotations from an Engineering standpoint.