[TillE]

You can get to a pretty clean modern C++ by convention and compiler warnings and static analysis.

Carbon is a completely new language, and that's the point. Part of the language design is making compilation a lot faster, for example, as well as features that C++ can't realistically implement, while retaining C++ interop. It's an exciting way forward if they manage to achieve their goals, and it would be a way to gradually migrate C++ projects.