It has benefits for those who has their samples on multiple PCs. The audio from these PCs need to be merged into one DAW and that can be done by various ways - 1. Gigabit LAN (with dedicated software) and 2. The conventional audio interface way. Since most samples are now running 24 bit, the traffic is going to be heavy.
But then again, most people wouldn't be using 8-10 PCs to run their samples - unless in film composition like Holywood. And if they are in a Holywood studio, USB is not going to be their concern as they are dealing with higher-end hardware.
For everyday sample user, the sample streaming bottleneck still lies on the HD speed. So no matter how fast the bandwidth is going to be (100 or 1000 times faster than current standards), it will make absolutely no difference since the HD cannot stream at that speed anyway. So you're right - for everyday people like us, it's the HD's speed that's the matter. If they make 15,000rpm more affordable or come up with even faster speed like 20,000rpm with 1 sec seek time, then things will change.