I think that PEP 450 is now ready for a PEP dictator. There have been a number of code reviews, and feedback has been taken into account. The test suite passes. I'm not aware of any unanswered issues with the code. At least two people other than myself think that the implementation is ready for a dictator, and nobody has objected.
There is still on-going work on speeding up the implementation for the statistics.sum function, but that will not effect the interface or the substantially change the test suite.