I don´t care about drivable cars per se, but I would love to have a pack dedicated to the culture of having a motor vehicle.
Having conversations about cars and bragging about them. I want to have neat industrial garage with expensive sports cars, the dusty underground garage with bar for motorcycle club owned by werewolves, one for the eccentric steampunk wizard who loves to reconstruct vintage vehicles (broomsticks with engine!!!) and just plain home garage, where teens come to party and parent teaches kids to change a tire.
I want to have races and car shows (and I mean RACES, not just loading screen, for cars and motorcycles, on the track and in the forest etc. For the shows, I am sucker for 50s´ cars, I would love rockabilly and pinup fashion, but super sleek sports car events would be awesome too), the whole pit crew need to be there (with skill bar, higher the skill the faster you are). New professions like car sales man, mechanic, reconstructor and race car driver. I want to have bets on the winner. Buying car magazines, import models having gigs (in sims 4 kid friendly style of course).
I would love new characteristics like adrenaline junkie, petrolhead/gearhead, deceptive (cheats on the sales, may try to sabotage the bets, slimy and greasy little weasel), show man (puts on the show in the ring, on the sales event, very charismatic).
I want the pack to have everything for every age, elderly people to drive slowly, teens buying their first car that is barely holding together, kids helping their parents changing the oils, first pit bike and falling off, anger from the fact that car seats are impossible to install, infants first time in the car.
But this is a lot for the Sims.. So I will see if there ever will be a car pack that is worth of buying.