You can add some functionality to limit scope and implement a caching system (which is also proposed here) to deal with M*N issues with a focus on keeping backwards compatibility. E.g. the caching is done automatically, the scope spamming control is a best effort solution based on static analysis (for example).
Moving from headers to modules is a fundamental change in how the language operates and is guaranteed to further break compatibility between compilers further. I worry that jumping to add these features to the language standard is premature and we should instead look further to optimizations within the preprocessor and linker to see if we can improve performance first.
Moving from headers to modules is a fundamental change in how the language operates and is guaranteed to further break compatibility between compilers further. I worry that jumping to add these features to the language standard is premature and we should instead look further to optimizations within the preprocessor and linker to see if we can improve performance first.