Most of my work is in countries where we we're using locally-generated spatial data e.g. health care facilities & their catchment areas. This requires joining to spatial files (usually ESRI shape files, sometimes GeoJSON, rarely KML). Very often the place names in the spatial files are different from place names in our other data sources so we need to do some level of transformation to join the data and this is a perfect use case for Tableau Prep. However Tableau Prep doesn't support spatial files.
This idea is for support for spatial files in Prep in the form of basic joins (inner, left, right, outer), unions, calculations, and support for outputting one or more spatial objects into an output .tde or .hyper file (i.e. formats that already support spatial objects). This would enable us to do in Prep what we can presently do in Tableau Desktop and other tools.
A separate idea exists for support for spatial joins (intersects) in Prep.