Prof. Wirth, when designing the Oberon language, adopted this heuristic: a new feature could only be added to the compiler if it reduced the time it took to compile itself.

Now this doesn't quite apply to cPython, of course, and even PyPy is written in RPython, not Python 3, (correct me if I'm wrong on that, eh?) so it doesn't quite apply to that either.

Every time newfangled geld like this comes down the Py3 turnpike I think of all the other Python implementations that either have to implement it also or get left behind: PyPy, Cython, Jython, Brython, Skulpt, Stackless, Pyjs, IronPython, PythonNet, MicroPython, Nuitka, ShedSkin, Transcrypt, etc., not to mention tools like Snakefood or PySonar or MyPy.

(I'll shut up now, you don't want to hear it. I read the tutorial on the new matching and by the end I found myself chanting under my breath "Cthulhu fhtagn! Tekeli-li! Tekeli-li!")