I think this would actually be a really easy fix. It's just a matter of telling clang to use "Objective-C++" rather than pure C++. Feel free to submit a patch if you'd like. Otherwise, I will probably get to it after I make some headway compiler bug fixes. This is one of those things we only need once we want to start using C++ interop in "real" projects, so I'll probably start working on it once the compiler is more stable.
Here's the post they made. While it's true that Google developers were the first and primary developers (especially in the beginning), there has always been a community of other developers around them, helping with reviews, discussions, etc. In the last few months especially, the community has grown and diversified. Part of the goal of this forum post is to push that even further. I'd love to find more developers who are interested in C++ interop. As I said in the post, there are several issues that would be great for beginners who are trying to figure out how they want to contribute to the Swift compiler. If you're interested in contributing, I'm happy to work with you (the indefinite you) to make that happen.