Unlike C++ the C language takes its freestanding mode seriously. In this mode there's no malloc() and so your string type can't exist. But today in freestanding I can write "ERROR" and get a string literal.

So that would mean either you abolish string literals in freestanding (making C worse) or you have a separate type for these string literals from the type for a expandable string.

Now, Rust pulls off the latter in my view fairly elegantly, but that takes a lot of sophisticated type features in the language including a DeRef and several AsRef implementations. In Rust these are general features open to other types, C could special case them instead, but that's still a lot of engineering for a small feature.

The result is definitely not the elegant language which can be described in a slim book. Maybe it's better anyway, but it's not C.

The rules around const don't compose with pointers inside structs, which makes this more complicated than you'd like. (I guess, just one struct for mutable and one for view of the string would work.)

I think there is sufficient membership in standard committee that doesn't want such "automated" features specially when touch memory allocation and freeing. And I too find it somewhat antithetical to C as language.

Still. Why isn't there a good quality library or set of libraries that would cover these features is my question.