We should just have a patterns sub-section under the AC: New Leaf board
This is your best bet. A separate pattern feature requires additional coding (and tbh isn't that fun or exciting anyway). Cool, but not necessary. Since this forum is heavily dedicated to Animal Crossing in the first place just adding a general 'Patterns' sub-board for the Animal Crossing category is a win-win. Easy to do, easy to manage, easily customized. Users can just create their own pattern galleries and run their own personalized Able Sisters.