I would like to chime in by noting that Rust's mature form is borne of a very specific scenario, which is the web browser, software so complex that the "zero-cost" element is more like "actually possible to optimize" in practice. And a great deal of that complexity is accidential in some form, a result of accreted layers.
And in that respect, it's not really the kind of software anyone needs to aspire to; aspiring to write programs simple enough that Zig will do the job is much more palatable.
I don't take issue with the "zero-cost" part -- Zig and C, like every low-level language, have that -- but with the non-abstraction-"abstraction" part, which is rather unique to C++ and Rust. Rust has become a modern take on C++, and I'm not sure it had to be that for the sake of safety; I think it became that because of what you said: it was designed to replace C++ in a certain application with certain requirements. It's probably an improvement over C++, but, having never been a big fan of C++, it's not what I want from a modern systems programming language. It seems to me that Rust tries to answer the question "how can we make C++ better?" while Zig tries to answer the question "how can we make systems programming better?"
Of course, Zig has an unfair advantage here in that it is not production-ready yet, and so it's not really "out there," and doesn't have to carry the burden of any real software (there's very little software that Rust carries, but it's still much more than Zig). I admit that when Rust was at that state I had the same hopes for Rust as I do now for Zig, so Zig might yet disappoint.
And in that respect, it's not really the kind of software anyone needs to aspire to; aspiring to write programs simple enough that Zig will do the job is much more palatable.