I've figured how to answer my own question. According to Guido's http://python-history.blogspot.com/2009/01/brief-timeline-of-python.html
, Python 2.0 came out in October 2000. According to Distrowatch.com, the transition between Python 1 and 2 on Debian occurred when woody (3.0) was released (in July 2002) or roughly two years after. My prediction was the transition between Python 2 and 3 will take 2-3 times as long, so the timeframe would be year-end 2012 through year-end 2014. It's unlikely that Python 3 will be the default on wheezy (7.0), particularly since Django with Py3k probably won't be ready by then, so we're looking at 2013 or later.