I have MANY suggestions for Sims 5.
For example, private schools. Let's say in the town there are two automatic schools, a private school, and a public school. The public school would work just as it did in the sims 3 (In my idea the map follows the sims 3 layout, not sims 4), children and teens would go to school in their everyday outfits. However, in the private schools, sims would have to wear uniforms. Also, just like with the Get to Work expansion for Sims 4, you could go to build mode for the private school and set up your own uniform. you could even set a tuition for every week, and if you wanted to you could set gender restrictions (not to be sexist, just to make it realistic). The way you would do this is to have a public school for anyone, one private school for just girls, and a private school for boys, or just one private school. Another thing to add on is having a separate elementary school, middle school, and high school. This would work if there were more age options (child, preteen, and teenager.) I also think they should add back universities. The only bug with this idea is that there would be multiple schools in one town, but maybe there could be another town simply for the University (such as in Sims 3) Also, to enroll in a private school a parent sim could use their phone, computer, or with the sims 3 map layout, simply click on the school. I think it would be cool to have a "tour" option for schools. Maybe the sims could even take their kids to the school, where they meet a principal NPC. One thing I'd love to see is where you could actually follow students to school, such as with the doctor, police, and scientist professions, but this isn't a necessity to me. I wouldn’t mind a university and private school EP instead of a base game.
My next suggestion is illness and injuries.
Sims 4 tried to add illnesses, but to me, they weren't very impressive. I haven't experimented with illnesses much, but I think we need more of a variety. Also, I'd like to focus more on injuries. Maybe clumsy sims could be prone to get injured at work or school. They go to the hospital and the doctor says they have to use crutches for a week or have a wheelchair. There could be many minor injuries, such as falling down the stairs and needing crutches. And maybe something severe like getting a concussion. Maybe if the sims injuries are so serious, they could be sent to the hospital, and their pictures would be greyed out. It would also be cool to get a hospital bill, and if they are in school, there would be a "Make Up Work" option the next day they went to school. Also, let's say a sim doesn't think they need to go to the hospital. For every day they procrastinate, the injury gets more severe. To explain this in depth, let's say a kid gets a concussion, and two days after the injury, they finally go to the hospital. Normally, the conclusion would last maybe 5 days, but since they waited to be treated it would last 7 days because they didn't get treated. I'm not sure if this is accurate at all to the real world, but I think some research should be done to make sure it's as realistic as much as possible. I wouldn’t mind this being in EP as it seems a bit complicated for the base game.
Another suggestion is clothes.
I was very disappointed in the difference between sims 4 and sims 3 CAS. We had many more options in Sims 3 and I would like to see those options return (Color wheel). However, I did like how Sims could buy outfits in the Get to Work expansion pack. It'd be nice to have that again in Sims 5. Also, I think there should be more stores, and that we shouldn't have to build EVERY store, with a minimum of 10 mannequins. I think there should automatically be a layout for clothing stores. Also... WE NEED MORE WEDDING DRESSES AND TUXEDOS!! I can only recall there being a couple of dresses that could be considered a wedding dress in Sims 4, and only one in Sims 3. We should be able to go to a store to buy a wedding dress, and maybe just evening gowns all-together. Also, since the details in Sims 5 are supposed to be more intricate, it'd be nice to customize more of the clothes, such as length of shirts, skirts, pants, etc. One idea is when going in CAS mode, you could click on a shirt, and there would be a customization mode where you change it to ANY color, maybe even add a logo or picture, and change the length or width. All of this would be done on a mannequin version of your sim. And when you're finished, you could click done, and even a "Save" option for future use.
I would also like to see more jobs. And I wish sims could have two jobs. (I know there was a way to cheat around this in Sims 4, but I still think it should be made easier to do in Sims 5.
One thing I don't want to change is Build Mode. To me, it was so much easier to build a house in Sims 4, and hopefully, they keep that format but add more to it. Also, I like how you could change the land plots in sims 3 "Edit Mode". I would really like that feature back.