If zig.build can alleviate the pain of building C/C++ projects, then it will surely to replace C in the future. So, IMHO, it's more important to get zig.build right than zig itself
and that's ignoring the nightmare of cross-compiling with gcc.
andrew kelley has talked about this[1]. his main point was about the number of dependencies you end up with compared to zig, where the standard library includes a high-level build system api. so your zig build scripts are written in ziglang and run by the zig compiler. no extra dependencies.