Async USB is just today's fad, USB3 is almost upon us. The spec allows for full duplex operation and so should function the same as firewire. Support is likely to be built into Win7 SP1, Intel has the controller side done and some manufacturers have already started fitting USB3 ports to their machines. So, the circus continues!
We shall be able to welcome a brand new raft of dac's built to take advantage of the native asynchronous operation and 4.5gb/s bandwidth. Doubtless they will all be 'the new reference in digital audio' and RA will manufacture a £500 USB3 cable! (BTW - the new spec for USB3 has quite stringent requirements for cable specs, the sort of shielding and geometry that will have the cable makers salivating!).
So, a new port to play with, a new computer needed so you can get a port to plug your new dac into, a new, or patched, OS needed to take advantage of it all. New player software for the new OS, new cables............. USB4 anyone?