I feel like it took me 2 weekends to "learn Rust" enough to make feature changes, and another 2 weekends to really "get it" enough to build basic abstractions.
I feel like it would take another week or two to learn some of the UnsafeCell/Pin/Generators type stuff, but none of that is needed for 95%+ of Rust code.
I think if you and your team just started learning Rust week by week, you'd find in 3 weeks that you're equally productive in Rust than your current languages. Especially given the code base already exists. Even just starting to learn Rust by writing tests (if there aren't) would be sufficient to improve that system rather than wait to hire or re-write it.
I feel like it would take another week or two to learn some of the UnsafeCell/Pin/Generators type stuff, but none of that is needed for 95%+ of Rust code.
I think if you and your team just started learning Rust week by week, you'd find in 3 weeks that you're equally productive in Rust than your current languages. Especially given the code base already exists. Even just starting to learn Rust by writing tests (if there aren't) would be sufficient to improve that system rather than wait to hire or re-write it.