AMK's Perl 6 and Python 3000 is an interesting read.

The total Python re-write, Python 3000, definitely isn't going to happen. Joel says that you shouldn't re-write working software at all, but Python is being re-written. It's just that it's being re-written one piece at a time.

I particularly like Tim's line - The "ain't broke, don't fix" philosophy is a good guide here, provided you've got a very low threshold for insisting "it's broke" <0.4 wink>.