Yes, it's not enough just to omit `__stdcall` from `DxcCreateInstanceProc` because widl inserts STDMETHODCALLTYPE into the header. We need a switch to prevent widl doing that, but we can do that later to avoid slowing the upstreaming work.
Right. Worst case would could probably strip STDMETHODCALLTYPE out of the generated header using sed, but #pragma push_macro/pop_macro is probably more convenient.
As for IDxcBlob I think it easiest to always call the IDxcBlob functions on them to avoid any incompatibilities.
It's a bit unfortunate. We could probably just create new blobs using D3DCreateBlob() to load the shaders into though?