Usually what happens is you make the choice to do a Rust port or rewrite, you maintain the C++ for a while and then eventually the Rust port matches it on perf then the will to maintain the C++ version falls off a cliff.

Seeing this at $DAY_JOB already. I suspect soon at $DAY_JOB the only 2 low level languages approved for greenfield will be Rust and Ada/SPARK.