What seems to be happening today is that outside specific domains like HFT, games, embedded systems or stuff like CUDA where C/C++ is the king, nobody wants to write new code in C/C++ or at least starting new projects in the language, while fervently migrating safety critical code to Rust.

Even in those domains there are efforts to do things in Rust, although it's unclear when Rust is going to be an actually serious/viable option.

I suspect C++ will become less of a "mainstream" language but only relevant in those specific domains. OS / Services will consider alternatives first.