vcruntime140.dll *is* a system library when installed properly, and if someone installs VCRedist then all the bundled ones should be ignored. Over time, I expect to see extensions appear that depend on vcruntime150.dll rather than 140.dll, so it won't always be shared by all extensions.

However, if someone has vcruntime140.dll installed and an extension requires vcruntime150.dll, they will get errors unless that extension includes the correct version. We can't ship currently-nonexistent versions with Python 3.5, and if extensions have to depend on what's installed then Python 3.5 extensions will forever be tied to MSVC 14.0.

GPL code should either statically link or recommend their users install VCRedist separately. I'm not going to compromise compiler version independence because of one license.

The uninstall issue is something I hadn't considered. Maybe we can special-case pip uninstalling it from the site-packages folder? *Paul* - any thoughts?