Both for committees and organisations asked to provide witnesses to committees, it is arguable that the very act of requiring those who select witnesses to think about their diversity (or otherwise), may itself encourage them to think differently, for example about the representation of particular groups, and that might in turn increase diversity further.
3. Improving (online) access to documentation for (particularly first-time) witnesses
Considerable work is already being put into:
Publicising the work of committees;
Seeking to attract evidence for inquiries.