I just noticed this in an industrial equipment magazine. Australian
company Fiberbyte Pty Ltd's "USB-inSync" technology "takes advantage
of data structures that are inherent in the bus protocol to provide
each device with a synchronous, phase-aligned clock, accurate to
within 10 nanoseconds anywhere on the bus." The patented hardware
works with any standard PC USB port, as all the new functionality
resides in the external USB device.

So far the company only sells industrial data acquisition devices.
Somebody should investigate licensing this for USB audio interfaces.

News Item:
http://neasia.nikkeibp.com/neasia/000848

Manufacturer site:
http://www.fiberbyte.com/

Loren