Since the Sims four now has a new team Fairies could be a thing

They can use the base game skills for these types of specializtions:

• Fitness fairies could change sims' morphology: gain/loose muscles or gain/loose weight, or they can make other sims energized (cross pack could be with Mt Komorebi: no accidents during skiing, snowboarding or rock climbing; another cross-pack could be with horses in horse ranch); they could also help sims reduce their tense or embarassed moodlets...more mischievous fairies could have the ability to "paralize sims" or reduce sims' energy needs drastically to make them fall asleep for a very long time 
• Social Fairies could have a spell that makes sims improve friendly relationship faster, or the opposite, make sims become ennemies faster; They could have a magic spell that improve mischief, charisma and comedy skills faster too. I also feel like they should have the ability to befriend every animals in the game instantly (except dolphins and fish, cause that would be the mermaids).
• We could also have Art fairies: they could improve the quality of paintings, books, wood sculptures, dishes and baked goods (cross pack with Eco lifestyle fabrication and crystal creation would be awsome imo and even any creative activities in the game like flower arrangments). Also, they could cast a spell on musical instruments to make them play autonomously and can inspire other sims by casting a spell so the sims would get an inspired moodlet. For a more mischievous fairy, they could also imbue an artwork with bad vibes which would make sims feel dazed, tense, angry etc...
• Mental fairies would influence any mental skills: logic, programming, research and debate + robotics (if university is installed). They can have a special spell to identify all the types of fish a sim can fish in certain areas; they could enchant plants so they would never have problems (not evolving cause island elementals can already do that); They could enchant spaceships so the upgrade would cost less money. And they could have a special spell to help students (kids, teens, univeristy student) finish their homework faster.
• And finally, I would like "Dark" fairies: unlike the mischievous fairies from the other categories, these fairies are specialized in dark interactions. They could curse a baby with an incompatible trait with the parents (for example a good trait for the child if the parent has an evil trait, etc...), they can summon gnomes anytime they want, they can increase the risk of accidents (cowplants, vending machines, pufferfish, meteorites, fires, electrocution, etc...). But as such, they could have a counterpart too, if they want to, they can give a compatible trait to a baby, they can appease gnomes, they can enchant protect sims from lethal accidents.

I hesitate for elixirs, cause the way they did potions for spellcasters was kinda unsatisfying, so if they go with elixirs, not only, I would like new bottle designs but also, they better have very original effects.