> that will let me iterate at the speed of JS or Python with performance of C or Rust.

Didn't Go already do that?

> I am so used to thinking that Zig, Rust, and the likes are only viable in niches where C is viable, but no. not anymore at least - once this linker and incremental compilation on other targets land, Zig will become THE C replacement

Yes, and it will still only be useful in the same niche that C is because the entire philosophy of Zig is to essentially be like C. You're never going to interate at JS/Python speeds with Zig because you'll always be wrangling with memory lifecycles, object lifecycles, etc...

Rust is significantly different.