By all means, if you have the time, send personal notes to each user as you do stuff… communication never hurts.
My concern is a) this does not scale b) my goal is to make life easier for moderators, not harder. And writing is hard. Quadruply so when addressing potentially thorny moderation issues. So from my perspective it would need to be more like a McDonalds Value Menu (gimme the #5, supersize) than “type words”.
Because the more you get mods to type new words, the worse it can potentially go. Many mods are not good at communicating, so having prefab content that gives them the best copy and the best possible outcome is preferable, by far, to an empty textbox.
That’s why the hide Pm encourages people to read the guidelines that we ship and edit their post as they fit based on those guidelines. The PMs are also specific to each flag type (off-topic, inappropriate, spam, etc).