USB 3.1 require a different front panel header than USB 3.0.
The USB 3.1 port interface is using the USB 3.0 pin set and more.
It is design to be backwards compatible (will explain later).
There are no official release of the specs for the USB 3.1 header yet (as of this writing),
But first motherboard with this is the ASUS ROG MAXIMUS IX FORMULA,STRIX Z270I/Z270G etc.
Length: 20cm
Connector1: Type-A USB3.0 Female
Connector2: USB 3.1 Front Panel Header