The reason why Swift isn't being used more is that the Build and Integration team at Apple forbids the use of Swift for any project that has downstream dependen

The reason why Swift isn't being used more is that the Build and Integration team at Apple forbids the use of Swift for any project that has downstream dependencies. This is because Swift doesn't support sending out its symbols, meaning any Swift project has to be fully built and compiled before beginning compilation of any of its dependencies. They're getting a little more lax on it now but we've wanted to use Swift for years and are totally unable.