Mini-games - I want every job to be a mini-game and most skill-builders (like chess, working out, etc.) to also be mini-games. These may be similar to one another within a discipline (for example, all musical tasks might be rhythm games regardless of instrument and all cooking tasks might be about short input tasks like Cooking Mama). These should have difficulty sliders for players based on the tasks too so that very young kids and casual players can still play. Finally, these must be designed well and be fun to play - the casual games market has refined mini-game gameplay down to a science so the mini-games have to be as good as the very best casual games on which their gameplay is based.
A better engine/better back-end design - even on excellent gaming rigs with a solid state drive, these games chug along with long loading screens and numerous game-interrupting bugs.
Expansions for boys (too) - while I know I'm not the primary market for The Sims and it is cool that there is at least one AAA title for girls, I have no interest in expansions that are about having an apartment in the city or going on family vacations. However, I'd absolutely buy an expansion that makes your home a space station and makes the jobs things like space-ship piloting, gunnery, and/or systems repair. You could go to "work" as a space captain (or crew member) and part of the fun could be recruiting crew members or using members of your family as crew so that you can skill them up. They could adapt this concept for a pirate ship, magical school, medieval court, or even a post-zombie survivor's holdout. This would also mean a lot more work and content in the expansions though, so I doubt they'd do it.
They should not cheap-out with teens. It was really weird to have to mouse-over teenagers to see if they were teens or thin young adults in the Sims 4. They should be 13-14 y/o teens visually to give the game variety - even if that means the artists have to do some more work adjusting animations and clothing skins.
First person with traditional WASD movement? Limitless town exploration? Larger cities? More socialization options? Shared world multiplayer? In-depth house building mechanics and a simulated real estate market?
Have they mentioned stuff like that? Your mileage may vary, but even if they added all of those features, I would not be at all interested.