What FPGAs support USB 3.0 super speed OOB signals?
Earlier in 2012, Xilinx had some support for US 3.0 PHY in their devices, but it didn't work out and they dropped that path completely. Recently there are new IPs on the market that uses the GTX transceivers on the high end FPGAs such as the V7 and some V6 and Zynq devices to interface with the electrical requirements of the USB 3.0. 

I am not sure if it is safe to design a PCB for 5Gb/s data rate of the USB 3.0 with only 2 layers. 

Here you have a link to the IP company that Xilinx works with:

USB 3.0 Device (USB3_DEV)