Currently, we get the reading level and time to read info after the message is send (even if using pre-flight feature). It would be awesome to have that info real time during the editing of the message.
We try to target at or below the 7th grade reading level (lots of our audience is English as a Second (or even third) language) and writing at that level is actually quite difficult. So seeing it live while crafting would be an incredible productivity booster. On the average email, that would save me easily 3-4 pre-flight sends, which in turn can represent significant time savings.