IMO the marketing as Rust as a C/C++ replacement is a bit misplaced. I think it's more accurate to consider it an alternative systems language. The tools/languages used in this space are a bit broader than C-family languages.
That's true, though systems programming is in practice dominated by the C ABI (great post on that here by the way https://drewdevault.com/2020/03/03/Abiopause.html). Zig does something quite special that puts it ahead of the crowd in this space; It can import and use C libraries as easily as C does (no bindings required), and it can itself be built into a C library, auto-generating the required C headers.
You are absolutely correct on the point of the C ABI. It's definitely the systems lingua franca.
Just finished reading the Zig cc article and I must say I'm also quite impressed. I'll be keeping an eye on the next Zig release--being able to eventually use it as a `cc` or `mvsc` replacement would be a big game changer. Having recently run the study of trying to cross compile a few C++ and GTK apps, I can really see the appeal.