I recommend you to connect USB2.0 D+/D- lines because if USB 3.0 enumeration was failed, it will be connected by USB 2.0.
You can see schematic best practices on AN70707.
When you are using DS4 as a shared link then, the 3.0 device connected (in your case, the camera) cannot be available for plug and play i.e the device has to be embedded on the board. But the 2.0 device can be removed and put back (which is done as per your schematic above).
Since you are using the shared link, you can leave the 2.0 lines of FX3 unconnected and make FX3 come up as 3.0 device always. But in the firmware you can make the change while calling connectstate API as discussed in the below KBA: