I really liked fragrances in Sims 3 even though it was a minor, and we sorta have it with flower arranging and they can totally expand on that. Similar to crystal creation's jewelry having both a moodlet and effects per fragrance, and depending on which packs you have (seasons/spa day/etc.). Fragrance can be applied as a perfume/cologne/lotion, used in a bath with bath salts/bath bombs/oils or with infuser/incense would all be great.
I personally feel Sims afflictions are already are enough to manage—even with a toggle option—having new/more personal maintenance to prevent or care for skin conditions seems like a bit much, but for pre-existing afflictions/conditions/negative moodlets—I think it be great.
Learning, experimenting and unlocking fragrance and fragrance combinations for either personal use to selling would be really fun. I love the idea of more gardening plants/trees. But hopefully it will be upkept with future packs as more flowers, herbs, etc. would mean more potential combinations.
More makeup/hair/facial hair CAS, would be great, vintage is a good idea but I think it be nice if they did makeup/hair/facial hair CAS, through various eras like 1900s through to 1950s/60s.