Regarding U.2, the better question is why nobody is making anything other than SSDs for that connection. It's 4 lanes of PCIe on a cable. At the very least, there should be an adapter that lets you put an M.2 drive in a 2.5" bay for better cooling.
i rather see more u.2 than the m.2 slots (made for notebooks soon a to slow standard anyway) the next ssd s from intel will focus on U.2 and not pci-e slot .
M.2 takes to much space on the motherboards also.
Cleverly implemented ideas on this board. The pins. massive socket, lane amt, clever implementation of the Dimm.2 slot... It's a beautiful board. I'm guessing most ROG consumers wouldn't see having one U.2 slot on it as a disadvantage, just my $.02 re that.