@Universal_Omega As I'm remembering, I did tell you on Discord, and you thought it was likely doable, if I'm remembering correctly, but basically like a filter, that includes all wikis, not just those as "uncategorised."
Make it either a separate drop-down box or a tickbox. When it's checked, category drop-down cannot be selected. Can potentially add other filter drop-downs for deleted wikis, inactive wikis, etc., that includes only those filtered wikis and excludes all others. Currently, you have sort by column, and this is rather sub-optimal.
Longer term, I'd like to add transclusion of the Special:WikiDiscover special page, so this can be transcluded onto actual pages, depending on drop-down filter options set.
This screenshot may help.