Christof,
This would require that there be a method of tracking methods and properties forward and backward in the class hierarchy. I'm afraid of the performance cost of that alone.
Interesting, however, is that if the child class is defined in code rather than with the designer, this not a problem. Because the code PROCEDURE Foo in the child class that is overriding the parent method code would become a method declaration in the child if the parent loses that method.