It's already happening, particularly with "Ladybird Browser adopts Rust" [0] being at the top of HN today. It's now feasible to quickly iterate on a system's design with a dynamic language like Python, and then, once you're happy with the design, have AI rewrite it into something like Rust or Zig. I can even foresee a future where we intentionally maintain two parallel implementations, with machine-defined translation between them, such that we're able to do massive changes on the higher level implementation in minutes, and then once we finish iterating, have it run overnight to reimplement (or rewrite) it in the performant language. A bit like the difference between a unoptimized debugging version of a project, and the highly optimized one, but on steroids.

[0] https://news.ycombinator.com/item?id=47120899