Thanks Matt. I believe that the required compiler versions that I proposed with PR #3969 basically support all C++17 language features. For some of the C++17 std library features, even more recent compiler versions may be needed. For example, std::filesystem is added with GCC 8, whereas the PR only requires GCC 7. And clang still does not support the parallel C++17 algorithms from <algorithm>. For details, you may have a look at Compiler support for C++17 - cppreference.com of course!
Note also that the PR still supports VS2017 (at least from version 15.7), even though I wouldn’t mind dropping that one either 
So I just want to say that PR #3969 is quite a modest proposal 