Ahhh, OK. I assume that is a limitation of the chip and/or phy that is being used rather than that of the software? If so, perhaps the DSO Quad should have a High-Speed (480Mbps) capable phy and chip.
As to the custom firmware, while I have only ever been involved with USB storage at that level, I think you can support multiple end-points if you set things up correctly.
I agree that it would involve a PC application to support the live data, but there are already some to choose from, like XOScope and others, although their code might not be capable enough or in good enough shape to work from. However, having been involved in Ethereal/Wireshark I have seen how something can start from humble beginnings and take over the world.