|The crowned one
I am enjoying reading this post, and the idea's behind it. Going right back to your original question my thoughts on the card historically speaking are as follows:
I think it is a Roman/ Christian based punishment that through time and "enlightenment" became a positive card.( as far as the cards go, yes Assyrians, Scythians, Thracians etc used it too...but tarotly speaking...), There are a few examples of Islamic punishments based on this, but I think they got it from the Christians as they used to hang cowardly knights upside down and beat them, Islamic people were sure to have seen this punishment… not quite the same thing as the hang man, but I am looking at a larger picture at this point.
I wonder if it is based on the reversed cross crucification, perhaps those few that survived had visions ( as unconsciousness on the reversed cross was very rapid, and generally so was death, it was considered being compassionate to crucify one upside down.) And there is St. Peter, asking to be hung upside down on a cross, since he felt unworthy to die like his Lord. These would lead to the more upbeat interpretations of the card: enlightenment, sacrifice, rather then the earlier idea of the card as traitor/ thief or punishment.
Then there is that Taoist thing of hanging upside down causing the essence of his sperm to flow into his brain…” there it is that the embryo of immortality is alchemically prepared.”( Eliade)
I believe northern Pagans used to hang and kill men in tree's as representations of the god Odin, Sir James G.Frazer talks about it in "The Golden Bough".
I think I am rambling ideas rather then helpful references and just generalizing, skipping all the symbolicness in the various versions of the card.
I am going to spend sometime going through all the links you all have suggested.