To me it seems like if bitcoin is not a currency, and if it's not security (investment contract), then is bitcoin then a commodity? Seems like you didn't mention anything about commodities, probably for some unmentioned reason. In The Good Wife the lawyers also argued that bitcoin was a commodity.
Bitcoin is a commodity under U.S. law. I have posted the legal analysis and included a discussion on U.S. regulations of commodities on my blog.
http://blog.bitcointitan.com/post/17789738826/what-u-s-regulations-apply-to-bitcoins-as-commodities