I probably won't be buying sims 5, if the game is ever made, I'm not convinced it will be though I am not convinced that it won't one day either.
However there are a few things that might make it tempting to me at least on sale.
1. Parenthood type traits already in the base game
2. Seasons in the base game
3. Open world but able to still run on lower end computers
4. Cartoony style
5. Free babies
6. Preschoolers, preteens, middle agers OR gradual aging where your sim hits every age 1,2,3,4 and gradually looks a bit older with diff activities locking./unlocking at certain ages
7. Toggle off for features like celebs, occult, strangerville style stories
8. Toggle off for build and CAS you'd never use
9. Still have the gallery
10. Small rework of traits /moodlet but not a full overhaul.
11. Story progression that you can control the amount of or flag certain sims it won't affect
12. Better family relationships and non mutual relationships.
13. More hobbies
14. Follow kids to school
