@Kersten thanks, but that's not it. I remember reading about a feature in an upcoming version of ArcGIS for Desktop (or perhaps ArcGIS Pro) that will allow the R script to be loaded directly as a script tool, without the need for any Python whatsoever.
@nmpeterson You may have read Take Away 10 at esri.com/esri-news/arcwatch/0515/… - it says that R in ArcGIS is for both the Desktop and Pro architectures. cc: @Kersten
