Halloween theme (not just one area)
Last Halloween myself and many other players were a little disappointed there were no global changes during the spooky season, only community parks had the Halloween theme so once you did your challenges there to get the Halloween currency I think its safe to say most players had no reason to continue skating those areas which means the rest of your gameplay felt and looked no different.
I'd love to see some global changes that gives us that nostalgic spooky season feel even if its just very small addons like pumpkins/jack o'lantern's scattered about and on door steps, cob webs, fall colors in the trees, more leaves on the ground, maybe even NPC's saying "happy Halloween", subtle windy ambience sound effects or leaves scattering, a slight color shift ect. I wouldn't expect all of those but even if its just one or two those would be awesome, It doesn't have to be over the top just small addon's like these can go such a long way for that Halloween feel.
These are slightly exaugurated examples but just giving an idea what I'm thinking about.