Broadly, this probably makes sense; there may be an open question whether this should be called vkd3d_shader_scan_descriptor_info1 or something else, and whether we should duplicate the original structure or just provide the extra information separately, but I don't currently have a strong opinion on that.
I do wonder about the reason for submitting this right now; my impression is that the shader reflection bits aren't in danger of being imminently released, so I imagine this is mostly intended to address the second point. That's a purely internal usage though, and wouldn't require introducing public API.