I have a bunch of different diabetes devices, from blood glucose meters to insulin pumps, that I want to connect so I can display the data on the Pixl.js screen. I see there are libraries for the various USB chips in these devices (e.g. Prolific, FTDI etc.) that were written for that shield, so I'm looking at porting those drivers. I already have JS code to read and parse data from the devices, but not from raw USB.
Maybe the HID USB driver would be a good start, as some meters use that to send data, and it can be used for keyboards too ;)