Ok, let's add to this, shall we? I didn't really say that they wouldn't come out when you were in main/blah, but that we would have the option to show Sub-Categories from Categories other than the one we're on.
So, to be more specific, the suggestion in
>>1 would be implemented, but the Sub-Categories of the Category you're not on would have this add-on, while the Sub-Categories of the Category you ARE one would be forced open.