I'd love a perma sort of spring/summer Sakura tree forest world (with the flower petals always falling flowing) for a sort of magical sense without magic. It could be Japanese, fantasy or an era themed world.
For me I like seasons in Sims, but I don't like actually playing out seasonal holidays in my game. Basically, I like L&D for a Halloween feel without being Halloween like the Spooky Stuff Pack. SE for winter feel without being Christmas themed. So I would like to see more of that.
But for seasonal items/stuff like autumn/fall/Halloween themed items there are great posts like this.