This may be possible with the current chart API -- I am not sure -- and it may be possible by playing games with stacking charts on top of one another, but ..

There are times when I would like to have different chart types on the same axis. For example a scatter chart and a bubble chart both on the same XY-axis. There are even cases where I would want to have a line chart and a bar chart on the same axis (even though a barchart doesn't have a numeric X-axis).