Feature request: A new facet system for `CoordRadial` to arrange different facet around a circle

[Yunuuuu]

Related to this issue, if such a method could be added to CoordRadial, we could also introduce a new facet type to split the circle plot into different radial segments, similar to this figure—though it would be quite challenging:

[teunbrand]

I share your sense that this is a cool idea, but I feel it is too much of a specialist option be included in ggplot2 and would have a better home in an extension package. One potential issue I foresee is that it is difficult to mix absolute units from e..g the panel.spacing.x theme setting with the relative ones describing the panels.