Hi Danny,
Very often there is a focus on STEM subjects, and not all research areas, so it would be important to try and be inclusive.
Open access to publications would be easier to capture in some countries at present, but the underlying data could very well be the future so that might be an area to focus on now while some governments especially in Europe are trying to figure out their policies in this area.
Clearly not every country yet has the capacity to start reporting on this, but many countries are copying others in terms of research exercises and measurement, open access policies are growing daily and so on, so now is a good time to begin to define what this could look like.