It would be nice to be able to do something like:
scale_shape_manual(values = list(raster_shape('file1.png'), vector_shape('file2.svg'))
There also needs to be some way to control the relative sizing of the shapes.
Also, it would be nice to be able to use shapes for legends, even when there are no point geoms. Like the example in the first answer here: http://stackoverflow.com/questions/13148404/use-image-instead-of-labels-in-ggplot2-legend/13148768
This sounds like a great feature, but unfortunately we don't currently have the development bandwidth to support it. If you'd like to submit a pull request that implements this feature, please follow the instructions in the development vignette.