Sometimes what's most important is not what you have but what you don't have. Zig doesn't have preprocessor macros; it doesn't have dangerous C-like unions (unless explicitly requested via "unsafe" constructs). Pointer arithmetic and casts are explicitly delineated as unsafe constructs, and are more easily avoided. What this means is that (unless the clearly demarcated "unsafe" constructs are used) all pointers in a Zig program are known, and cannot be created "from nothingness" (as in C).

In addition, Zig, while about as simple as C, has the same expressiveness as C++, not to mention its exceptional build capabilities.

I don't know if all that would prove sufficient to one day replace C and/or C++ -- replacing incumbents is always an uphill battle -- but Zig is the most revolutionary (rather than evolutionary) low-level language we've seen in a very, very long time. It offers a completely different approach to how low-level programs are to be written and built.

Because Zig is so simple, how revolutionary it is can be missed when you look at one feature at a time, and can only be appreciated once you consider the whole: The mix of simplicity and power, and the eye toward tooling.