I was thinking last week how I wish the hub had a larger hub world. Have a giant island as the hub and have the island be influenced by Japan, California, Hawaii and other Pacific beaches. Have the main city in the center of the island be like Tokyo meets San Francisco. You could skate, rollerblade or bike through the city incorporate the ink mechanic to it as well as some sort of trick system. Maybe blasting ink on the side of walls will allow you to skate on them. Have different outlets, battle locations, single player missions, minigames and collectibles scattered throughout the city. Allow you to create your own clothing outlet where you can create and sell your own clothes. Also incorporate some sort of graffiti system with the ink to make some cool graffiti art on buildings.
....I think I just thought up Nintendo's GTA.