WikiVoyage has a small but clever extension to do quicker lookup of pages in additional content namespaces if no namespace prefix is provided. So if we used this for Commons, and configured "Category:" as an extra lookup namespace, you could type "Low quality chemical diagrams" and it'd pull up the category of that name immediately without the full-text search being loaded.
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Thoughts? Would this be a useful improvement for Commons in particular, even without autocompletion? I suspect it could help reduce some of the category/gallery pain.
This sounds like a very good addition, yes.