Another subtle consideration is that with long-lived, highly-backward-compatible languages like C++, you'll have a bunch of people on your project who still wri

Another subtle consideration is that with long-lived, highly-backward-compatible languages like C++, you'll have a bunch of people on your project who still write C++ like it was ten or twenty years ago (because that's when they learned it), and so bring down the code quality of your project. Whereas choosing a new language (like Rust at the time) means that everyone who claims to be able to write it at all, is working from the same, recent set of language idioms.