USB3 with fewer wires
I could not find any information regarding initial synchronization for USB3.  The best idea I could come up with is insulating the UTP pair from the old USB and trying it out.  

So I covered the two center data pins on my USB3 hard drive cable with some kapton tape and plugged it in.  The computer negotiates with the drive fine.  No longer initial sync than normal.

It is likely that a 6 wire USB3 cable would work.  4 for LVDS pairs and Power and Ground.

However, most cables have a separate ground for each LVDS pair.  This is to give return current paths other than the pair. This is helpful for signal integrity, just like how return current actually flows in the ground plane under LVDS pairs, not in the other pair, on a PCB.

So you are actually loosing only 2 of 10 wires.