I wonder how easily arcs can be identified. I'll try running the transcripts through a topic model this evening.
If you're interested in tools, Mallet (http://mallet.cs.umass.edu/) is a fairly good place to start, and the original LDA paper by Blei, Ng & Jordan (http://machinelearning.wustl.edu/mlpapers/paper_files/BleiNJ...) is a great academic starting point.