They aren't even suggesting you would rewrite any code. And you wouldn't lose any performance nor would you gain any either. And the noone has mentioned anything related to "compiler modularity".
Originally Posted by porkbutt
The most direct effect of this would be that faster compilation and smaller and more logically constructed ASTs for clang. Presumable faster linking as well.
Long term it could make C/C++ much move convenient to use, and less patching shit together with preprocessor macros which is what we do now. No performance loss anywhere.
Those are very very good reasons why you should "screw with it".