I have not yet met such a case...

I think the two are fundamentally contradicting - one is trying to blur the difference, and the other is trying to make it obvious. The issue is that object which have type specific features are not really polymoprhic WRT to each other, but only WRT to their superclass.

Any code that deals with such a case should probably either try to deal with smaller chunks of functionality, talk to the delegates directly, or make the program work a bit harder by making a better factory.