This is a fairly simple request, though I don't know how complex it would be to implement. We already have positionToLocal() and positionToWorld(), both of which are extremely useful. However, it would be significantly more useful if we had rotationToLocal() and rotationToWorld() to go with them. As it is, trying to get two objects to match rotations is a pain in the arse, and borderline impossible for many purposes without a more robust rotation/vector library.