Well, the problems don't start after 20 years but after 5 or so (depending on the size of the codebase and the rate of the application's evolution), and the rea

Well, the problems don't start after 20 years but after 5 or so (depending on the size of the codebase and the rate of the application's evolution), and the reason there aren't many large and oldish Rust codebases isn't because the language is too young for that (work on it began twenty years ago, and it's been stable for over a decade); that's middle-aged for a programming language. When C++ was of a similar age, there were thousands of >1MLOC programs written in it. One reason is obviously because when C++ was of the same age, there weren't as many suitable high-level alternatives, and people just don't pick a low-level language for most large applications anymore. But most Rust fans at least on social media, have not actually had much experience with it or with low-level programming in general; I'm guessing most haven't worked on Rust projects with more than 10 full-time people on them (this isn't normal in the industry, BTW, as a lot of software lives in large programs). And again, there are people who can certainly live with these issues, but they are real, and many certainly find them troubling.