Sure you can juggle around a little with references to namespaces to try and restrict access, though I have yet to see a waterproof method — for example in the sample-code in the livedocs, all you have to do is find an instance of a valid class and pass its reference to beMyFriend(), after that nothing stops you from calling makeMyDay() from whatever class you please..

What I was trying to say in the start of my post was that there is no explicit (and foolproof) way to configure namespaces to only be applicable/accessible to certain classes.

see: http://livedocs.adobe.com/specs/actionscript/3/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=as3_specification114.html

other use cases where namespace can be useful are unit tests, where for ex you need to set some internal value that you can not access directly in the class, but you want to setup to test a particular thing

Regarding your second point, I think you might be overgeneralizing — while in some cases the need for such a solution to a problem may be an indicator of a glitch in your design, the idea described in this post is way too abstract to state that for every situation it is applied in there is a problem with the design.
On top of that as a developer you don’t always have control over your superclass, it may be from a third-party precompiled library or a class you can’t change the structure of because it’ll break other existent functionality.

Secondly the need for this seems to me to indicate a case where inheritance really shouldn’t be used. If you need to circumvent the implementation of your super-class there is most likely something wrong with the design in my opinion.