I have a couple thoughts: First, on all Expansion packs, note, we do not like nagging reminders and free stuff we could get elsewhere. In TS2 I remembered some guy would come up to your door with a free computer, and in TS3 we got a University Mascot bugging us on day 1, along with a free time machine. Features like this are more interesting if I have to do some steps to get/purchase the time machine. And the University Prep kit is in the buy mode catalogue. Keep your free earbuds to yourself, and let me buy them too, TS4.
University: It is understandable that you'd need to give us some base game careers, but being able to, for instance, join the medical field is unrealistic without a degree. Maybe a rabbithole university could be base game. That way you could expand it by allowing us to follow a student to college in an expansion pack, but keep cross-pack compatibility for all of your expansions and their careers.
Occults: Whether you add these in one pack or many, I honestly almost never play occult sims. Though I do usually like the often Gothic/ worn furniture that comes in these packs. Players like me do like options to turn off the occult features. I don't like going to university and seeing many students running around with fairy wings, and such. In TS4, I don't have any of them yet, but I've seen too many videos where vampires have come out to your regular sims worlds, and It would break the emersion for me.
Celebrity: These are kinda like occults for me. If a setting could, say limit them to a certain world, atleast, I'd be happy. Atleast when they're not in their "Casual mode" with the hat and glasses. That way my sims won't faint over a celeb while getting their groceries, or whatever. And yes, I'd love to be able to go grocery shopping.
Rabbitholes: I don't mind if the base game comes with a bunch of rabbitholes. But I would like it if, with later expansion packs, these very rabbitholes could be opened up and become more active parts of the game. For instance, In TS3, we got rabbithole restaurants in the base game, and in a later store kit, thingie, I think, you added a "run your own restaurant" thing, but these were separate from the rabbitholes. I'd suggest it that if you got xyz expansion pack, suddenly when you go to enter a restaurant, it actually opens up as an actual lot and you can buy the business and run it if you choose, or just leave it and the system would run it on automatic if you don't. So there would be actual food there if you didn't click it and say hire a chef, which I remembered was an issue with the TS3 version.