Defining portraiture is interesting - although I also find that as I go on I am less and less drawn to definitions.
Categories from an aesthetic viewpoint (as opposed to technical) do worry me a little - there is often something that doesn't fit. Also, some work straddles, or defies boundaries. It can be like squeezing something into a box that is really too small, rather than placing something in a nice big box, and carefully placing packaging around it.
(I would really like a place to discuss film types, lighting etc. relating to a particular 'genre' - for want of a better word. In some ways I would find categories easier for this).
Following with interest, though..