Regarding USB3.0. As far as I understood it is mandatory as an ISA switch (there are rumors it could be Ryzen, but its still not decided yet) will require USB3.0 to be supported. Without USB3.0 you can't get no mouse or keyboard working, even when you attach USB2.0 or 1.1 devices. It has something to do with the USB3.0 mode that has to be fully supported in order to activate its legacy protocols.
As I know, modern Ryzens ( for example Ryzen 9) still have one native USB 2.0 connection for legacy firmware compatibility. It is enough to boot with keyboard. And southbridge often have his own USB2.0. So it is no showstop.
Of course, there can be other serious reason for 3.0. Or simply it is good idea have at least USB3.0, SATA3 and PCIe NVMe support with fast CPU.
AmigaOS3: Amiga 1200
AmigaOS4: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad