This is kind of a misconception about categories. [[:Category:Prussia]] does make the category visible, in the sense that you'll see [[Category:Prussia]] in the text. But it doesn't actually put the profile in the category. It only refers to it. That's why you won't see the categories where they're supposed to be.
So, if things are redesigned so that categories are more visible, it'll have no effect on things like [[:Category:Prussia]], because that's just text.