There's at least one reported case of a PCIe multiplier card working with the Pi...

		hausen on Dec 22, 2020 \| parent \| context \| favorite \| on: WiFi 6 gets 1.34 Gbps on the Raspberry Pi CM4 There's at least one reported case of a PCIe multiplier card working with the Pi4: http://labs.domipheus.com/blog/raspberry-pi-4-pci-express-it...