I think that now we have a permanent Mall, and that there is a costume shop, they should make other rooms in it interactive and actual shops. Here are some ideas:
Sport Shop, which would be located on the top left, where it would be where you buy sport items, jerseys, furniture and backgrounds relating to sports.
Puffle Hat Shop, which would be located bottom left, near the enterance. Here, you could buy all different kinds of puffle hats, available during the years of 2011-2015, and some that didn't appear in the game at all.
Smoothie Shop, which would be moved from the Coffee Shop to the Mall. It would be found in the right bottom end, where there would be a cafeteria as well. You could buy smoothies, backgrounds and even earn pins by playing the Smoothie game.
Igloo and Furniture Store, there the furniture catalog would be available. However, this time there would be seasonal pages on the furniture, and the catalog would be in a different style, similar to real life. Plus, there would be a "Create-A-Furniture", similar to the custom furniture section before, except you can choose from bed, chair, igloo, carpet, window or curtain.
Cafe is where you can work as a coffee server, or at the desk. You can work at a new game called Cafe Cashing, where you would have to work and get the right orders to penguins. If you get 5 done in a row, you earn "Cafe Pin", 10 you get "Cafe Background", 15 would be the Cafe Worker Hat, and 20 would be Cafe Worker Suit.
Grocery would have no catalog, but instead a way to earn money. You could go and collect some fruit and veggies and click on them to put in a bag, then you pay it with real coins. After, that bag with the food becomes a pin, which would be the exact one.
School Supplies would be available during the School parties, and it would change each party.
Any other ideas?