Hans de Goede, a developer contributing to the QEMU project, has a blog post about some of the USB work that's been going into QEMU. Namely, there's USB 2.0 support and USB over network redirection support. Gert Hoffmann is the other developer and he's been cleaning up the EHCI support so that it can be merged (the code originally appears about one year ago), with this USB redirection over the network being based atop that tree.
Those wishing to experiment with QEMU USB2 support for now need to manually build libusb, usbredir, and a separate branch of QEMU. QEMU then also needs to be started with the usb-ehci device for gaining the USB2 support. Hopefully we'll see the support merged to master in the near future.