If anyone wants to play, I'm the author of Classifier4J which is a very old Java rest classification tool, which also includes a text summarization engine. I believe the algorithm in c4j has been ported to Python and is available in NLTK (https://groups.google.com/forum/m/#!topic/nltk-dev/qV9e5TsCB...).

I did a bit of testing of the java version, and it was pretty competitive with commercially available summarizers at the time.