TechPowerUp saw a pure 12V power supply from FSP at last week's CES 2020 show. This new model is designed for Intel's upcoming PC specification, which gets rid of 5V, 5VSB, and 3.3V in favor of making everything 12V. This gets rid of the bulky 24-pin ATX power connector. The PSU supplies 12V to the motherboard, which then uses onboard VRM and DC-to-DC switching to output lower voltage to devices that require less than 12V like SATA storage devices.
The pure-12 V PSU has only two domains: +12V and +12 Vsb. What this means is a goodbye to the bulky 24-pin ATX power connector. The PSU only feeds 12 V to your motherboard, which uses onboard VRM and DC-to-DC switching to put out the lower voltage domains, including power for your SATA storage devices. The 24-pin connector is effectively reduced to a new 10-pin connector that only has 12 V and 12 Vsb cabling. Other cables include 8-pin EPS connectors for your CPU VRM, and 6+2 pin PCIe connectors for your graphics cards. EPS and PCIe power are purely 12 V-based standards already. The 5-pin connector is less than half as thick as your 24-pin connector, and 2 pins wider than an EPS connector. Some of the more premium PSUs may user thicker gauge wires for this connector.
It's an interesting concept but whether it will get adopted remains to be seen. Over the past decades, we've seen various new proposal but so far ATX is still standing strong.