Add style option to series data options
Allow series to be customizable through css classes. This would make it easier to customize the styling of a series, (ie. change the color) by changing values in a css class.
Implemented as of Highcharts 5.0.
If all chart elements at least had specific classes, then anyone could optionally style the chart completely with CSS. That seems like not a big effort just to at least have the chart make sure all elements have a known class? The chart could still use JSON config for those who wanted that.
It would require a separate set of CSS for the SVG and VML implementation. My advice is that it is by far easier to keep this in a unified JSON options environment.