Not sure if this has been requested.
I often have to integrate CG content into an existing photo and while the VFB postprocessing stuff is great, it would be even better if you could exclude background and/or objects from post processing.
Once there's a shadow catcher material available, the workflow will probably be to render against a screen mapped ground plane, so having the option to exclude that object would be necessary to be able to judge if the CG content is matching the backplate.