If we were going to create a Lingua Franca for such a purpose from scratch, it would probably look very little like C. It would probably look like a much reduced subset of Some compiler IR, or Haskell. We would want something that is typesafe and lowers trivially to an AST. As the barest of table stakes, a language with any undefined or implementation defined behavior whatsoever is obviously unsuitable for this purpose. After all, we need a wide variety of compilers to be able to easily generate their own IR from it, and for them all to guarantee exactly the same behavior when they do. C seems close to the worst choice possible.

Edit: Haha, I realized I invented WASM again. This happens frequently...