Trash80toHP_Mini
NIGHT STALKER
On Pi4, USB is implemented over PCIe.
Exactly, folks were getting at PCIe on RPi4 by de-soldering the USB3 Controller to get at PCIe
On CM4, the PCIe bus is exposed, allowing you to add USB or another interface. (PCIe<->PCI<->NuBus?)
PCIe to PCI is a done deal with simple boards employing the ASM1083, which looks like the only active component on the cards.