A rear camera on a tablet is such a non-feature for me that it never even crosses my mind that any of my tablets have one.
So genuinely, what's the overlap between people who use iPads as the worlds clumsiest cameras and iPad Pro buyers? I know that it might seem unconventional to put a higher-spec camera on a lower-end device, but my guess is that iPad Mini and base iPad buyers include a larger fraction of people who use the camera. If there's an iPad Pro buyer who doesn't have a phone with a decent camera it will be because they don't care about that, so I don't see this selling any extra Pros.
So genuinely, what's the overlap between people who use iPads as the worlds clumsiest cameras and iPad Pro buyers? I know that it might seem unconventional to put a higher-spec camera on a lower-end device, but my guess is that iPad Mini and base iPad buyers include a larger fraction of people who use the camera. If there's an iPad Pro buyer who doesn't have a phone with a decent camera it will be because they don't care about that, so I don't see this selling any extra Pros.