There was one, the ASUS Sabertooth 990FX Gen3/R2.0, but the main reason is that there is very little difference between the 700, 800, and 900 series chipsets, basically they're just rebrands which mean little besides motherboard support of a CPU. Even the Radeon Pro Duo and the new nVidia Titan don't saturate PCIe 2.0 x16, so it's not like you're bottlenecking there. PCIe 3.0 allows for better power usage, and lower costs because they need fewer lanes to do the same job. There is also a strong indication that AMD will skip right to PCIe 4.0 with Zen, given a prototype Zen server board has already been shown PCIe 4.0 Means Motherboard x16 Slots Will Have 16GT/s and 300 Watts At The Slot - Legit Reviews
When we met with AMD for the Zen processor launch last week at IDF, we were shown the AMD Naples server board and it had four PCIe slots on it. We also noticed that besides the boards main ATX power connector there were four 8-pin power connectors and two 6-pin power connectors. It looks like two of the 8-pin power connectors and both of the 6-pin power connectors were for the graphics. So, it looks like those PCIe power connectors will just plug into the motherboard instead of the discrete graphics cards.