I like to call it semantic C programming. Essentially the simplest use case is that C syntax highlighting would always be 100% accurate if the code is correct (most current editors used some kind of regexing to parse a language syntax of highlighting purposes, which is a losing battle IMO). Another use case is that if I download someone else's C code, I don't have to read it in their coding conventions; my editor would translate it to my preferred coding conventions on the fly.
However an llvm-editor-C combo is much more powerful than that (it seems, though I still have to refine my ideas). Essentially it's the orthogonal direction where you could take C, compared to taking it towards the OO enhancement resulting in C++ language.
In this way you could add language features on top of C. For example you could setup your editor to understand your OO constucts and generate corresponding C code. But then you could add features to C that even C++ does not have.
Based on my discussion with other people, by this point in the discussion, lisp starts to get mentioned. And for that reason alone, I wish to learn lisp properly someday to be able to have a better understanding of this idea.