I like the water park idea. I think it would be good to have something similar to Disneyland, as in, the fact that sims 4 worlds are split into neighbourhoods and Disneyland is similarly split into different areas, I'm not saying it has to be the exact same as Disneyland but I just think an big amusement park with a resort would be fun, you could have a water park/marine neighbourhood, an amusement park neighbourhood, and a resort/golf course neighbourhood, it would also be family friendly with mascots like the freezer bunny, I just feel that Granite Falls and the jungle adventure are aimed at older sims, I don't really see any of my child sims wanting to visit them but I think they would be excited for a something like this.
Also I would love for a beachside resort or sandy get away, with the ability to swim in the ocean and maybe bring back sailing boats and row boats from sims 3. You could add in swimming with dolphins and shark cages, be able to build sandcastles, make hammocks, collect seashells. And like Go to work where you can own a clothes shop, you should be able to buy and run a resort or B&B.
I also think a safari world would be a lot of fun. Of course they would have to make vechiles so you could tour the area. It would be good to have animals as well - zebras, lions, giraffes, elephants, even if they were NPC and not playable, this would make the vet job introduced in pets more exciting if you had a chance to look after these animals as well. Maybe also the option to start a safari lot or zoo in your home neighbourhood.
I Just think looking back on the previous games and what options we had (Sims 1 Vacations – Winter Wonderland, National Park, Sunset Beach. Sims 2 Bon Voyage - Tropical Island, Mountain Campsite, Far East. Sims 3 World Adventures - Shang Simila, Champs Les Sims and Al Simhara, Sims 3 Island Paradise. Sims 3 Store - Monte Vista, Sunlit Tides) it just seems that we haven't been given much of an option from EA so far.