If ATX is being redesigned today, than it will not become better but worse for end users. Things like moving major power supply to the motherboard - for instance like in the 12VHPo standard.
Why is this worse? Voltage step downs are cheap and not too hot in this day and age. I'm all for simplifying power distribution in my systems
Not to mention that most of the power provided by modern PSUs come from the 12V rails. The 3.3 and 5V rails are almost vestigial at this point, no hardware actually runs directly at those voltages, so removing them would not have any negative effect.
Because it moves complex circuity to an already very complex and expensive PCB, making it even more expensive. A power supply is likely to outlast multiple (re)builds of a desktop computer; a motherboard is likely not - especially not Intel motherboards.
Change something, it's bad. Don't change something, still bad. What's the solution?