Given the discussion until now, Jean-Claude, what is it that you're trying to accomplish with this debate? Are you up for proving that the MOP is "wrong"? You have repeatedly indicated that this would be your opinion. If so, are you trying to create a new version of the MOP that would not include class redefinition hooks? Or are you up for creating a new Lisp or a new Lisp object system that is inspired by the MOP but somehow different?
Sorry Hans but I just got a "come to Jesus" moment and therefore had to consult the scriptures directly.
What do I find in the AMOP, #'cl:update-instance-for-redefined-class and #'cl:make-instances-obsolete are nowhere to be found in it!
I see this as a sign.
One finds #'cl:change-class and #'cl:update-instance-for-different-class inside AMOP but not the other two.
I would then be tempted to drop almost half of my case after all.