It's is a tedious work during refactorings to maintain the signatures in the headers.
Once I have modified the signature of a function I would just like to press a shortcut to apply the new signature in the header.
It could be done automatically, though overloads can confuse the picture.
The Ctrl+Shift+Space feature is somewhat similar and already works, in case of overloads I could get a popup to select the overload to modify.
Inconsistent signatures could be underlined, like this:
long myfunction(int goodpar, int wrongpar, int goodpar2);
Ok, I know taht the second case wouldn't be that easy when (member)function pointers are used.