I think this rewrite is driven by the well-known safety challenges and long-term maintainability concerns with C/C++, not performance per se. Of course rewrites from existing high-level languages to Rust can result in huge performance gains.
> Allowing background functions and concurrent functions has been a goal for many years. I have been nursing a long-lived branch which allows full threaded execution. But though the changes are small, I have been reluctant to propose them, because they will make reasoning about the shell internals too complex: it is difficult in C++ to check and enforce what crosses thread boundaries.
> This is Rust's bread and butter: we will encode thread requirements into our types, making it explicit and compiler-checked, via Send and Sync. Rust will allow turning on concurrent mode in a safe way, with a manageable increase in complexity, finally enabling this feature.
