My list would probably be,
-Preteens, for this I would like it more for The Sims 5 but, if they do add it for The Sims 4, I would enjoy it. For preteens I would like them to mainly have small crushes/love interests, were they could possibly have their first kiss. Along with a few other ideas people have had.
-School, like everyone else.
-University, almost identical to The Sims 3, but not as many rabbit holes.
-A Teen stuff pack or game pack, again pretty much what everyone wants.
-A Nightlife Expansion pack, like The Sims 2, but more about dating like online dating (like in The Sims 3), chemistry system, likes and dislikes, a more improved romance system.
-A Generations expansion pack, even though we already have Parenthood, this one should not only shape your children's childhood but your adult Sims, from Babies to Elders. Similar to The Sims 3 Generations.
-Previous families from previous Sims game, such as the Pleasants, the Brokes, and many others.
-Vacations
- A Supernatural expansion pack, I would love to see witches, fairies, Bonehilda, Mermaids. I never liked werewolves or zombies(from The Sims 3 Supernatural).
- An Into the Past expansion pack, mainly on the Medieval times (which I would love to be almost based on Game of Thrones in a way,) and on the 1900s.
-Along with maybe returning families but with some of the worlds from previous Sims games, such as Pleasantview, Veronaville, and Strangetown.
I probably have more but this all that I have on the top of my head at the moment. A lot of the things that I saw, was probably better than my list.