for crypto-mining you'd convert a single PCIe slot into 4 x1 PCIe slots - or just have a board with 12+ x1 PCIe slots. I'm not sure what magic goes in to PCIe, but i do know that at least one commodity board had "exposed" PCIe interface - the Atomic Pi.
anyhow the GPU would sit on a small PCB that would connect to an even smaller PCB in the PCIe slot on the motherboard, via USB3 cable. My point here is merely that whatever PCIe is, it can be transported to a GPU to do work via USB3 cables.
anyhow the GPU would sit on a small PCB that would connect to an even smaller PCB in the PCIe slot on the motherboard, via USB3 cable. My point here is merely that whatever PCIe is, it can be transported to a GPU to do work via USB3 cables.