This is cool. It'd be nice to be able to write bitstreams to FPGAs without needing the vendor's tools. I wonder how similar the protocols are between vendors (ie. Xilinx, Altera, Actel, Lattice, etc.)? Is this supposed to also work with the flash chips that are used to program FPGAs on power on?
Also, even though it is not directly related to kernel, it might be a good idea to push toward Ethernet instead of USB as interface of choice for these things.
USB is brain-damaged hardwarewise, it requires registration with USB consortium ( which is why majority of such projects use FTxxx instead of native USB support within microcontroller- which brings up new set of headaches) and above all, it is not insulated, that is, your PC and the device that you want to debug, read or program, have to share GND and signal lines. Which can be awkward or outright dangerous.
Why people dablle with USB on these things is beyond me.