Articles would show up in the category list under their piped titles.
All subcategories would be visible on the first page of the category, rather than segregated alphabetically based on how the individual articles are segregated.
"There are 200 articles in this category." would not be used to mean "There are 200 articles on this page.".
It would be possible to get a list of the leaf articles.
Categories and articles would be combined into one namespace. (I realize this isn't going to happen.)
What links here
It would be possible to filter the results by namespace.
There would be a "related changes" link on the "what links page".
It would be possible to get a list just of the redirect pages.
