If you're going to exploit a privilege escalation vulnerability from your app, why not just grab the most interesting parts of the /data partition while you're at it?
Sure why not. I wasn't implying that a zero day that allows surreptitiously recording the phone screen is the only shitty thing that can be done with your phone with a zero day.
Also, it is possible for a zero day to break specific privileges (like screen record without notification) rather than root.
