A community center.
The community center would be a place to throw specific types of parties and depending on the type of party you are throwing there, the interior decor changes automatically to fit the occasion. For instance, let's say you want to throw a child's birthday party. You go the normal route through your phone, choose "child' birthday party" then under places to have the party "community center". When you travel there you arrive at a pre-decorated location that has everything you need to throw a child's bday party. Maybe there is an arcade area, a jungle gym, a bounce house, and a magician. There are balloons, streamers, cake, ice cream, pizza, the whole shebang. There can even be a pile of presents like in TS3 Xmas party, where the kid can open presents.
Sometimes I like throwing bday parties at home, but sometimes it feels like too much of a hassle to decorate and none of the sims appreciate it anyways. At home my guests usually end up just watching tv or getting on the computer. If the community center is pre-decorated for the occasion it would only include activities that would fit in the specific type of party theme. The community center could be used for all kinds of other occasions such as toddler, child, teen, young adult, and adult bday parties, prom, weddings/wedding receptions, bachelor/bachelorette parties, baby showers, funerals, etc. It would be nice too if there could be options as to the type of party you want to throw, like casual or fancy wedding reception.
Some examples:
-Prom: I really miss having my teens being able to attend Prom like in TS3. It was always something I looked forward to and was really the only time my teens actually dressed up. I liked that my teen would have to get to know other teens and then choose someone to ask to Prom.
Ideas for Prom:
Teen sims would get a notification alerting them prom is coming up and to ask a date (if they choose to).
Teens can then click on a closet to choose their prom outfit.
Prom can be held at the community center instead of a rabbit-hole. Theme of prom could be chosen at random by the game like Under the Sea, Hollywood, Yule Ball, Masquerade, Casino Night...
When teens arrive at the prom, all other teens in their town are their also dressed up and the community center is decorated based on the theme.
The Prom is set up like a regular party so everyone stays until the party is over.
Different activities/interactions can be there for the teens to interact with like: Drink punch, spike punch, ask date to dance, ask _____ to dance, take prom photo with_________, etc... There could be good and bad interactions that pop up where the sims can choose how they are going to act at the prom. If they choose to do "bad" things they could have the potential for getting caught/in trouble.
They could also still get picked as prom king or queen and get a crown like in TS3.
Although now that I've written it all out it would probably need to be in Generations EP.