When you want to reproduce a real face or body, it's easier to have reference photos like front, profile, that we can overlay with transparency.
For example I have a photo of me (in front) and I would see it when my model in CC is in front. Of course many photos could be added, under other angles, and I could fit the size of the photo to character size. So if I zoom on the face of the model, the size of the photo changes accordingly (but if I change the size of the photo, visually my model doen't "zoom"). It's just a static overlay with transparency which is visible only under a given angle. Also, no perspective in this mode, to avoid problems when I pan the model.
For me it's the most urgent feature to have.
I thinks that it could be done as an post-process effect? Anyway, thanks if you also think that it's a good idea to have it asap.