[zokier]

> It'll have to be high-speed USB2, and will almost certainly need to be some kind of custom driver, as I doubt you can do some kind of super baud-rate of 16,000,000+bps

The venerable FT232H claims "data transfer speeds up to 40Mbytes/s":

http://www.ftdichip.com/Products/ICs/FT232H.htm

I'm not sure what is needed to actually accomplish such rates. Might be easier to do it with USB-enabled MCU. Either way, I wouldn't discount the standard USB classes too early. I'm "pretty sure" that you should be able to push some tens of Mbps through USB-CDC class.