ESR seems to care really strongly about concurrency things being "primitives" in the language. Why? There's nothing wrong with them being part of the crates ecosystem. Maybe in 10 years the crate you chose won't be under active development, but it's not like crates will just mysteriously break once they reach a certain age. As for the language itself being stable, sure, a program you write today might not compile using the latest compiler in 10 years, but it should still compile using the last 1.x release, so it's not like you won't be able to compile your project in 10 years.