I've gone down this route of thinking many times. Inevitably, as soon as I think of all of the features that I would want in C, I simply end up with a language that's not C any more... for precisely that reason. C isn't that kind of a language; it's a high-level assembly language and little more. Most of the things that C is lacking, it is by design, because of performance reasons and/or need for fine-grain control of the machine.

As another respondent mentioned, there are other languages that fill that need (C++, D, Rust, Nimrod), basically all of the systems languages that are designed to do C's job easier and safer (but probably not faster).