With cppfront, Sutter is explicitly not trying to create a successor language. His goal (like TypeScript to JavaScript) is to provide a complimentary, parallel language which provides complete forwards/backwards compatibility with C++. His hope is that (like TypeScript), the languages and communities evolve together. Any other technology that involves developing new tools, migrating code, or lacks completely frictionless interop will be inherently fragmentary. It reminds me of the classic XKCD comic: https://xkcd.com/927/