What's the idea?
My idea is to allow the axis to be moved to the top of the chart.
In most situations the axis needs to be at the bottom but for some it would improve legibility by moving it to the top this is not currently possible.
Example 1: A vertical bar graph that will always show negative values would be much easier to read if the category titles were above the zero line.
Example 2: Gantt charts can benefit from having the axis on top - this allows the user to immediately understand the date range being shown without having to look down to the bottom.
If the required measure is duplicated and then the chart is turned into a dual axis chart it is possible to 'white out' (make the same as the background) the bottom axis labels leaving the top axis labels visible. This is not perfect as it still means the axis is present and takes up precious space while doing nothing of value.