One of the biggies missing for charts (from my perspective) is the ability to click and filter by values on the charts. Most BI tools do so and it's an easy and intuitive way to navigate up and down through the data. Similar to what "analyse schema" does in Compass, but much more flexible.
Not sure if my use case would be covered by this effort, but I'd like to be able to navigate to an arbitrary URL when clicking on a value. For example, if I have a scatterplot of movies, I'd like to be able to click on a movie and navigate to IMDB/RottenTomatoes. Or if I'm plotting sensor data, I'd like to be able to click on a datapoint and navigate to webpage with more details for that particular date.