The Python core developers value the evolutionary approach, and don't tend to get carried away by ambitious projects like a massive revision of the language and interpreter infrastructure (Parrot).
Martijn Faassen, in a comment on Titus Brown's Perl is Dying?
If I'd spent eight and a three-quarters years designing and implementing a backwards-incompatible revision of a programming language (see Will Python 3000 Break My Code?, from February 2000 -- and that's not the earliest reference to Python 3000, either), I'd set my sights on goals slightly more ambitious than shuffling around the core library, changing the syntax slightly, and improving Unicode.
I'm not criticizing Python 3.0 by any means. It's a decent, modest improvement on a decent, modern language. Just don't mistake it for anything revolutionary, and don't pretend that it didn't also take almost a decade, even with Googlebucks-funded development.