I would be quite concerned about us storing any content that a user entered before they published their revision. In the case of tone check, that they have entered before they have even expressed any intent towards publishing it.

As a boring hypothetical example that wouldn’t involve any bad motives from the user: imagine that I make a mistake and paste my phabricator password into VE, and because it’s a nice long phrase it turns out to be both a tone issue and indicate where it might be useful (“DLynch’s totally awesome phabricator password!”). Naturally, I notice this before I submit my edit — but maybe not before I’ve seen a tone check for it. I wouldn’t expect that submitting my edit after I’ve removed that accidental paste might result in it getting stored on Wikipedia servers and be viewable by sufficiently privileged patrolling users. Even less so that it might be stored and be available if I didn’t then publish the revision.