Can FPC 0.5mm cause usb 3.0 interference inside itself?
Wow, this is an ambitious approach I think! I am already scared to do such an appraoch on USB 2.0 high speed. I think using a 2-layer flex cable (bottom side as a ground layer) instead of using a standard FFC cable will allow you to match the 90 ohm impedance and to get much better results. But I have to admit that I'm not a high-speed layout specialist as well.