This was status-completed for a short time, but a few tricky bugs surfaced causing a bit of confusion in moderator messages. It's a little harder to (ab)use drafts than originally thought and we had to turn the feature off.
However, since this is implemented and just turned off, we're going to try and fix it for inclusion in our latest round of moderator tool enhancements and fixesour latest round of moderator tool enhancements and fixes which should wrap up within the next two weeks. keep this in mind as a major feature if / when we're able to give the messaging system an overhaul. As it's currently put together, we simply can't wire it up as easily as we hoped.