But even then, that is still using PCIe lanes. Wonder if a custom protocol on a direct, short link would be even faster (think HyperTransport, or its equivalents).
PCIe 3.0 with 16 lanes is 16GB/s bidirectional non blocking. What scenario's would require >32GB/s? For those 0.0000000000000000000000000000001% of the time does the cost of a proprietary solution outweigh the simplicity and economies of scale in using off the shelf components?
It all comes down to cost vs benefit.
The bridge chip is actually "not" required.
PCIe spec differentiates ports from lanes. It is "possible" to have a PCIe controller route lanes to two ports on the same expansion slot. Support is essentially non-existent. Most (all?) motherboards assume 1 slot = 1 port. If a dual GPU used that feature it either wouldn't work or only 1 GPU would be usable in non-compliant motherboards.
If at some point in the future most motherboards supported routing 2+ ports to the same physical slot then there would be no need to use a bridge chip. Each GPU would simply connect via 8 lanes. One irony is that those GPU wouldn't be usable PCIe1x slots (i.e. extenders).
