I think an amusement park is likely given that it's been teased in a number of surveys (like OP said) and also the fact that Sims
Freeplay also has an amusement park/carnival feature and there's usually a lot of content overlap between TS4 and freeplay.
In Sims Mobile the amusement park feature comes with a carousel, roller coaster, ferris wheel, a bounce house, a juggling stage, and carnival stalls (kissing booth, fortune teller, high striker), and popcorn & cotton candy stands.
I can see similar features coming to TS4 in a game pack. There could also be a new juggling skill to go with the juggling stage.
