Ed,
I don't think I would classify them that way. First of all the RFA files in the imperial or metric libraries are the family elements or components not sub families.
I guess the folders could be called the family categories, similar to the listing in the Settings menu for Family Categories and Parameters, but the RFA files would definitely be classified as the Family file containing the various types associated with that family.
Is this for an upcoming article? Look forward to reading it.
Mel Persin, AIA