The biggest problem of Python is that it lacks the experts that could write those fast runtimes, and it fails to attract them after the Python leaders declared the GIL to be a non-issue.
Furthermore, Python is not really memory prudent either. PHP is much better in that regard (very fast startup time, fast page render times, but a rather different approach).
> "... I'd welcome a set of patches into Py3k only if the performance for a single-threaded program (and for a multi-threaded but I/O-bound program) does not decrease."
Unfortunately, experiments thus far have not succeeded to meet these requirements.
There is some work being done by the Gilectomy project to try and meet this bar as well as some other requirements currently though [2]. But it is currently grappling with the afore-discovered performance issues that come with removing the GIL.
Also at PyCon 2016, Guido himself mentions the Gilectomy project and it's potential consideration (if it works) for Python 3.6+ [3].
So when you say Python leaders declared the GIL a "non-issue", I think you are oversimplifying the actual reality of what removing the GIL means and why leaders (like Guido) have been reluctant to invest resources pursuing.
[1] http://www.artima.com/weblogs/viewpost.jsp?thread=214235