Conditional appearance panel
It would be great if you could use some conditional logic together with appearance panel, and possibility to pick individual characters/words (first/middle/last 1, 2,...characters). And also possibility to combine several styles under one appearance, together with some input panel for user interaction). That would make it possibility to do more repeat things that you now need an action for but instead could use a style. Because actions I have tried tend to have a lot of errors to them, sooner or later. So maybe this could become a more stable option and I can see how this can make Illustrator even more useful.