Board Thread:Support Requests - Getting Technical/@comment-28905095-20170204175614/@comment-9605025-20170204232914

Yes. Unfortunately, this still isn't natively supported. The generation of the page list and images for the gallery are all done by some portion of MediaWiki that does not have an interface for use on other pages. If what you want is at all possible, it would probably involve a custom JS script and/or an additional MediaWiki extension.

As for the gallery, in your case it shows all the pages because you haven't yet reached the limit. However, once you do, it will only show a random subset of the pages in the category.