> the worry is by the time it reaches v1 Rust will have consumed the space that C/C++ used to

Given that Rust is quite an old language now and its adoption is still so low, I don't think that should be much of a worry, although that doesn't mean Zig will be the option of choice, and not stabilising is certainly not a good sign. At Rust's adoption rate, a language that hasn't been invented yet and that would show a more normal rate of adoption for a popular language could easily overtake it.

> There is also the issue of will people actually code by then.

Now that could be a bigger issue. :)