One improvement I'd like to see is a simplified error message for mismatched overloaded calls. If you make an overloaded call for which the is no matching conversion or if the conversation is ambiguous the compiler will "helpfully" dump a list of possibly matching overloaded function signatures. The list can be hundreds of lines long. For example, when you try to pipe a class to std::cout that doesn't have an std::ostream &operator<<(std::ostream &, const X &).

Perhaps instead of dumping the complete function signatures it could show one function signature followed by a list of types accepted as the second parameter. Since the signatures are otherwise the same. Such improvements could also reduce template error spew.