We should not have to pay for cars, since they are a base game feature.
Instead of a purely romantic GP, I'd like a general Relationships GP that fleshes out ALL relationships to make them more meaningful - friendships, enemies, family ties etc. It would be great to add in one-sided relationships, a chemistry system (determines how sims get along in general, not just romantic) and a turn on/off system (romantic). Ways to sabotage other sims' relationships and lives should be added as well (spreading rumours, talking smack, giving bad advice, manipulation etc) and the gossip mechanic from TS3 would be amazing.
But above all, life stages should be fleshed out and family play made more interesting via a Generations-like pack. I think a lot of the boringness from family gameplay is bc of the boringness of children and teens (nothing to do and could use a lot fleshing out in general).
For children: more playground objects (that teens can interact with too), more play interactions that aren't tied to objects (tag, make believe etc), games like hopscotch and jumping rope etc. Board games that the card/DWTL tables can be switched to and the whole family can enjoy. Play bake ovens and the ability to "help out" with cooking/baking under adult supervision. Functional piggy banks, small stands to sell anything they made or found, not just lemonade (but definitely including!).
An update to school to include field trips, extracurricular activities (sports, ballet, debate etc) that interact more with the actual school instead of being a mini career, participation trophies, studying for tests etc.
Teens get more angst, interactions, mood swings, acne from low hygiene instead of it just being aesthetic, obessive phases (crushes on sims, celebrities and fictional characters), PROM, rebellious activities, existential crises, more visual differences from young adults etc.
Pranks, prank calls, slumber parties.
Toddlers are great, and I hope they get some extra stuff to do to make them even better (tea parties with toys, TS3-sized teddies etc).
For elders, I hope they go all-out, since they have been largely ignored in general in the sims. Stereotypical elder activities (not limited to elders but there if you want it, ex. knitting, bingo, scrapbook making etc), canes, reminiscing with others, on photos, on their own etc. Special "grandma/grandpa's cookies", special advantages and features to mentoring others, pension, special cranky elder interactions like scolding youngsters, ranting about good old days, chasing sims off their lawn etc. Also, some sims might get an existential crisis in their elderly years about having regrets, while others might get a satisfied buff about not having regrets.
Babies are freed and have more interactions, stations, toys etc. More cradles and bassinets, toys that can be slotted into them, and ability to change their outfit (even if it is limited to picking the colour of their onesies and diapers). Vomiting.
Adults get more gameplay like mid-life crises, enhanced work performance from experience, balanced with slower progress in learning new skills completely from scratch etc. Stressing about new wrinkles and checking them out in the mirror, enjoying partying etc less (except if having certain traits or a mid-life crises), back pain, ability to put away a nest egg for when they're an elder (ex. hiding money under the bed or "opening a nest egg account" via their cell phone/computer).
More family identities: cousins, nephews/nieces, step brothers/sisters/parents etc. and the ability to set these relationships in CAS.
And: better mourning!!! Funeral home lot that functions as both a cemetery and a destination for funeral "parties." Proper funerals with speeches, eating appropriate foods, discussing sims and their lives, mourning (or celebrating if a sim had a bad relationship with the deceased) etc.
