I appreciate the depth of your response; the original reasoning makes sense, and as Python 3 tells us, it is very hard to get people to use your new version if you break enough old code.
This seems unfair to Python 3. The Python community, including the developers of Python 3, have not been encouraging people to migrate to Python 3. In fact, it was never in their roadmap for people to migrate immediately. The common wisdom has always been 'When starting a new project from scratch, if all the libraries you need are ported, and you won't need backwards compatibility down the road, then use Python 3. Otherwise, use Python 2.x'.
It's quite difficult to get people to use your new version when you actively tell them that it's probably not a good idea right now.
