rMaps ichoropleth with custom map/shp
Solution 1:
Various people on recordnotfound.com asked the author to reply to this thread (on recordnotfound.com). I got in touch with the owner of the rMaps project, Ramnath. He suggested that there is a new project that provides an enhanced feature set: http://github.com/rstudio/leaflet
Here are more details about the leaflet project: https://recordnotfound.com/leaflet-rstudio-35205