ATX was designed to run Pentium Pro processors, not Core i7s.
No it wasn't. ATX was designed so manufactures
and consumers could buy an ASUS motherboard, Intel CPU, MSI graphics card, Crucial RAM, LG DVD, Seagate HD (and now Samsung SSD), power them all via a Seasonic power supply and install them all in an Antec case and insure (1) they will physically fit and align with applicable mounting holes using ATX standard screws, (2) electromechanically connect with compatible ATX standard connectors, and (3) electrically connect with ATX compatible compatible voltages.
Motherboard power control has gotten more and more complex as hardware requires less and less voltage.
Yes, but it still belongs on the motherboard, not inside the PSU because the motherboard/chipset/socket is what determines which CPU and RAM is compatible with the board - not the PSU.
They tried to replace the ATX standard once and it failed miserably. Remember BTX? Manufacturers and us consumers rejected it almost entirely. I say "almost" because consumers do like cases that support bottom mounted PSUs.
We will NEVER have a "replacement" for ATX because it will be impossible for the major makers to come to a consensus on a new form factor. And notebooks are a perfect illustration of that. It is
because Sony, Acer, IBM, Dell, HP, Compaq and the others wanted to have proprietary designs to (1) force users to their brands and (2) keep prices artificially high, there is no real form factor standard for notebooks.
And who suffers the most for that? We consumers! Why is there virtually no build-it-yourself notebook industry? Because there is no ATX standard for notebooks that allow consumers to buy parts from different component makers and be certain they will fit and work together.
So again, there will never be a replacement form factor standard for PCs. And there does not need to be either - not until we consumers are willing to give up total control of our PC configurations to Dell, HP, Acer, and Lenovo.