My guess is that this is requested a lot by OEM manufacturers like HP and Dell who want to reduce the number of wires and save a few pennies this way and get less complaints about proprietary / custom connectors on their power supplies.
HP is known for using custom connectors in their workstation systems for example, Dell also has some power supplies with custom connectors.
It's an OK move but it's sad that Intel didn't have the guts to go further and work with power supply and motherboard manufacturers to innovate further.
Seems like they just stuck to 12v standby and 12v to power everything.
I would like to see a new revision of the standard to introduce 20v (-10% .. 5%) (to allow possibility of powering a system from DC In barrel jack using 18.5v adapters common in laptops), while keeping 12v for backwards compatibility.
20v is standardized in USB, so having 20v and 12v would make it possible to use USB connectors to power a monitor for example, or fancier external storage.
It shouldn't be very hard for the psu to include some kind of microcontroller or something with a usb 1.0 or 2.0 connection to the system, allowing the system to communicate with the psu and enumerate capabilities ...
For example i'm 12v only, i'm 12v and 20v, i'm 20v only (motherboard could have this tiny chip by the DC In connector and detect 12v or 18.5v..20v and pretend it's a psu with 12v only or 20v only ... useful for small systems with an APU that consume 40-60w max... power them from a 90w laptop adapter or a 200w atx psu)...
psu could also say current on each voltage, total wattage, indicate if the 12v is derived from 20v using dc-dc converters..
motherboard can query and get number of fans, fan rpm, may even be able to tell psu to adjust fan rpm (but psu would have the final say as in motherboard can't override psu's safeties ... if psu controller needs to spin fan at 50% to keep cool, user would not be able to force fan to shut down)
maybe support rgb if the power supply has leds inside...
With just two output voltages it could be possible to have a current shunt on each 12v or each 20v pair of wires ... or worst case per 2x4 connector (eps, pci-e 6/8 pin etc)...
Some would argue 5v should also stay as an option , as that could allow future very low power laptops and tablets to be powered completely from a 10-15w 5v laptop adapter but nah, lots of usb chargers have option to go up to 12v or higher and dc-dc converters are tinier and tinier and more efficient.