Absolutely doable. The modern i7's have 40 PCIe lanes. If you built a quad processor system you would have 160 PCIe lanes... Have a look at the obscene number of PCIe lanes in modern server architectures.
The bigger issue would be memory bandwidth, but I think that could also be engineered around.
Edit: SuperMicro sells a system with 8 PCIE 3.0 x16 + 7 PCIE 3.0 x8 ... 184 lanes not counting the other onboard peripherals. So it basically exists minus the Apple form factor.
The point was less about the form factor and more about the number of PCIe lanes that can conceivably be available and the associated memory/bus bandwidth that is possible.
Haha, I see. That's a blade center with 8 "PCs", each supporting one PCIe x16 card and some supporting an additional x16 card (with only 8 lanes connected).
The bigger issue would be memory bandwidth, but I think that could also be engineered around.
Edit: SuperMicro sells a system with 8 PCIE 3.0 x16 + 7 PCIE 3.0 x8 ... 184 lanes not counting the other onboard peripherals. So it basically exists minus the Apple form factor.