Currently you can put a workplane on a face, but the orientation (U and V-axes) are based on something to do with how the face was originally created, and that will not be obvious to users days, weeks, or months later. As a result, the orientation can seem arbitrary. There is an option in the Setting to specify that the "Up Direction be along the Z-Axis", but that still not be what is needed for every face.
Add a property to a face which is the "horizontal direction". This should be something that can be set and inquired.
