When will we see the first PCIe 4.0 motherboards and should I wait for these if I'm going to get two-way SLI GTX 1080's?
Two PCI 3.0 x8 slots wouldn't bottleneck two 1080's, would they?
No, no bottlenecking whatsoever. Far from it. As for PCIE 4.0, you'd be in for a really long and pointless wait