Seven years ago someone at Google estimated that there was 2 Billion lines of code in production to support Google Services [1]. Given this was seven years ago the number is probably much higher now and a large chunk of it is C++. Clearly any replacement language for C++ has to seamlessly (as primary design goal at least) consume and update this gigantic C++ code base. Nobody is rewriting all of that from scratch. That pretty much rules out Rust, Golang and various other languages which provide a thin "extern C function" level compatibility at best. Would be interesting to see how the language progresses.

[1]. https://www.wired.com/2015/09/google-2-billion-lines-codeand...