Yes, the backend for Swift for Tensorflow will still be C++. The difference is that it will be the compiler (at compile-time) and not some library (at runtime)

Yes, the backend for Swift for Tensorflow will still be C++. The difference is that it will be the compiler (at compile-time) and not some library (at runtime) that will be mapping Swift native operations (instead of library calls) directly into the Tensorflow graph API. It's a much more sophisticated frontend, but there is no porting of the backend to Swift.