When I look at the datasheets from an SMSC USB3.0 capable hub it seems
the USB3.0 superspeed paths are seperated from the USB2.0 paths so a
USB2.0 device will not be faster.
http://www.smsc.com/Products/USB/USB_Hubs/Standalone_USB_Hubs/USB5434B/Download
I thought you might know as you actually design USB hubs.
So far I only used the USB2.0 ethernet and ethernet / USB hub combos
from SMSC. The people responsible for the software in those projects
however did extensive tests which show the chips are stable under
load.
Doing a USB3.0 layout may not be trivial. Routing traces carrying
5Gbps on FR4 is doable but there are some pitfalls.
All overheads included, useful transfer rate over USB 2.0 is only about
30 M/s. USB flash drives are near this limit at least for read speed.
Several simultaneous transfers through USB 3.0 hub would definitely be
big advantage.
It seems it will take more work to get it going if you insist on using
[email protected] flash drives. USB3.0 flash drives are already widely available.