While Visual Studio 16.8 (<-> MSVC 19.28) has _just_ been released, I think it would be worthwhile to consider upgrading the compiler toolchain that's used to build the CPython windows binaries, particularly before the release of 3.10.

That's because many libraries (e.g. numpy/scipy) are stuck to the same compilers as CPython for ABI-compatibility, and generally, MSVC is by far the lowest common denominator in terms of C/C++ compliance, cf. https://github.com/scipy/scipy/blob/master/doc/source/toolchain.rst

For example, dropping python 3.6 support in scipy should finally enable them to use C++14/C++17, since python 3.7+ is built with Visual Studio 15.7, which has essentially complete support, cf. https://en.cppreference.com/w/cpp/compiler_support & https://en.wikipedia.org/wiki/Microsoft_Visual_C%2B%2B#Internal_version_numbering.

However (& as far as I can tell), the windows compiler version for CPython hasn't moved since the release of 3.7, cf. https://pythondev.readthedocs.io/windows.html#python-and-visual-studio-version-matrix (I know that's not an official page, but vstinner can hardly be considered a questionable source), and every release without upgrading the toolchain means another year of waiting for the ecosystem to unlock more modern C/C++.

The reason why Visual Studio 16.8 is particularly interesting, is that MS has for a very long time not paid attention to C compliance, and only recently completed C99 support, with C11/C17 following in 16.8 (though as of yet without optional aspects of the standard like atomics, threading, VLAs, complex types, etc.), cf. https://devblogs.microsoft.com/cppblog/c11-and-c17-standard-support-arriving-in-msvc/.

Looking at the table from https://github.com/scipy/scipy/blob/master/doc/source/toolchain.rst, it would be cool if we could add the last line as follows
===================   ==============   ===================
CPython               MS Visual C++    C Standard
===================   ==============   ===================
2.7, 3.0, 3.1, 3.2       9.0           C90
3.3, 3.4                10.0           C90 & some of C99
3.5, 3.6                14.0           C90 & most of C99
3.7                     15.7           C90 & most of C99
3.8                     15.7           C90 & most of C99
3.9                     15.7           C90 & most of C99
3.10                    16.8           C99, C11*, C17
===================   ==============   ===================
* [comment about lack of C11 optionals]