I'd like to see a white rabbit NPC added somewhere in a world, that sims can follow down a rabbit hole. With the sims 4's fondness of using rabbit holes, it would be such a funny meta thing to put in and would be in line with the more surreal stuff they did in earlier sims games.
Like in the pop ups the sim could even think about how cool it would be if others get to see what they see. Going down the rabbit hole could give a few possible unique rewards not found elsewhere that are not common objects either.