The recent ISO C++ committee meeting in San Diego ended yesterday, and marks the C++2a feature freeze. Barring anything unexpected, this means that the committee won't accept further proposals for new features.
This means that we've a reasonable upper bound on C++20's feature set. Here's hoping modules make it to C++20. (And non-type template parameters!)
Visual Studio 2017 has modules available, on an experimental basis. I've been playing around with them and find the usage rather intriguing.
Now, maybe MS has implemented the use of modules different than the ISO C++ committee may lay out if/when adopted, but it is an interesting feature I too would like to see added.