I started playing the Sims when 4 came out so have no experience with past versions. However, I've seen images of packs from those games that I wish we had in Sims 4. Particularly the Renaissance game.
As for more that could be done with Sims 4 for future updates, I can think of a thousand ideas. One I would most like to see is something that includes a billiards table, pinball machines, and other types of games you might find in a bar and/or home. As one who builds and creates sims only for fun (I don't really play my characters much) I would really like to see the designers come up with furniture, window treatments, and color schemes that actually make sense. Firemonkeys do it beautifully with the Sims Freeplay so I don't understand why everything in sims 4 seems so chunky, clunky, and cartoonish. Any update that included height options for CAS and clothing color choices that make sense would be a huge gain for the game. Lastly, I wish they would provide more large lots for those of us who like to build mansions and castles, and fix the camera shot angles for gallery so some of the best large lots don't have cliffs, rocks, tress, or other buildings blocking half or all of your property in some shots. No one wants to bother looking at your build if they can't see the main image because of a monstrous tree in front of it.
Some ideas for theme packs: Alaskan Adventure (bears, whale watching, seals, penguins, ice fishing, seasonal length of days, etc.) Celtic Village with stone streets, Kilts, Celtic dancing, instruments (bagpipes, harp, tin whistle, flute, fiddle, etc.), leprechauns, quaint inns and pubs. Cirque de Sims Circus tent, circus travel train, performing elephants, camels, monkeys, lions, tigers, bears, performer trailers, sims learn and perfect acts like tightrope, trapeze, trampoline, animal training, bareback riding, shot from a cannon, etc. Out of this World. While there are rockets, aliens and some sci fi elements to play with in Sims 4, it would be fun to send sims to planets in other galaxies far far away to live, where they can build homes, have jobs, wear local way-out clothing, have strange new pets and avoid encounters with indigenous dangerous creatures.
Not my favorites: Journey to Batuu was a disappointment because I wanted to build homes and have my sims live there but I have hardly played it because I'm clueless what to do with a world where I can't build. I had high hopes for Strangerville but that one fell flat for me also. Del Sol another dud. You'd think a community that housed celebrities would have a gated "Hollyweird" section with several huge lots and a wider range of items to build with but the offerings were less than dazzling and the colors, yikes. Have you looked at celebrity homes lately? I've yet to see wallpapers in the colors and styles in this game.
EA, let's get up-to-date and get your creators to come up with some realistic elements and futuristic places.