Feature request: Add different shapes to legend

It would be great if you could configure legend shapes for different data series. For example, for a line with markers it would be a line with marker on it, for a column it would be a square, for a line without any markers it would be just a line, for scatter plot it would be circles. You could see on examples below how it might look like:

I can imagine one example where it will be definitely useful - black and white printing. It won't work with just columns or just lines, but it will be exactly better than now.