Official C Challenge ①

Task:  Come up with an extension to the C programming language.  Provide a clear description of the extension, and a code sample that clearly shows what the extension is intended to do.

Prize:  (Winning criteria are not specified.)  The winner will have his extension featured in the C11 language standard.

My entry:  ... Sorry, I think C is perfect in every way already.

>you don't know how big your object is based on its type
Not everyone has telepathy, or knows the source for foreign/future/closed code which will use the sizeof() or "guess".
You've never written portable, scalable code?