Yes, add conformance tests for the new ntoskrnl functions and usbd.sys, and break the patch up a lot...
Conformance tests should consist of a driver and a program to load it. I do not know other method to call functions from ntoskrnl.exe and usbd.sys on Windows. But I have a problem with building drivers with MinGW. I was able to create a driver which is loading on Wine with manual editing of PE header but it does not work on Windows and I do not understand what should change to fix this. Did somebody build NT drivers with MinGW?