I greatly question the concept of the Sims 4 having the "perfect platform" for fairy representation, unless you (as the player) are very flexible and understand just how limited the Sims 4 really is.
Truthfully, I believe one of the biggest problems the developers likely have in regards to bringing fairies to the game is the fact that a lot of the abilities they could or would develop have already been done... some things repeatedly.
I have no idea how easy or hard a task it would be for the team to make it so fairies can minimalize things, but I think if they did, the items would probably have to be very limited - like objects that are only decorative. The minimalizing of a Sim would also be very limited, considering all Sims of humanoid shape are required to be the same height for physical interactions to work smoothly. At best the Fairy Sim would probably be able to minimize themselves, but not really be playable. So if you are fine with your fairy Sim going poof and appear as a sparkly sphere of light to go into a specially object (dollhouse, cute garden sculpture, tiny "fairy house" - kind of like a bird house) to do a rabbit hole action (like sleep, eat, party, use the restroom...) I do not really see them being able to produce something better than that.
Healing could be interesting, but by what means? Ghosts and Spellcasters have abilities that are like healing in terms of helping other Sims with needs, so that wouldn't really be unique or new...
Blessings sounds cool (and curses?) Those already exist in certain ways as well when it comes to Ghosts, Spellcasters, mystical wells and the treasure chests from Jungle Adventure.
Nature magic sounds like a rehash of the Green Thumb reward trait, the Great Soil lot perk, the Micro Home perk from Tiny Living, the Spellcasters Floralial and Herbio spells, Patchy from Seasons, the extra help you can get from birds, rabbits and chickens in Cottage Living... and even with those perks your plants will still turn into dirt piles.
Fly and levitate objects... Fairies being able to fly in the Sims 4 would likely be them levitating above the ground like Ghosts or Servos, turning into a smaller form and shooting up into the sky like Vampires. Levitating objects would likely only be a parlor trick that resembles an object being used for spectral whoo-hoo or slumber. "Flying" an object would likely be similar to teleporting, but the ability would be new to the game and could be useful depending on what can actually be moved.
I doubt the Sims 4 would be able to grant a Fairy Sim that ability to shapeshift much of anything. On a Fairy Sim it would probably be like how Aliens, Vampires, Mermaids and Werewolves have two appearances or forms. On other Sims, it would probably be like a rehash of a Spellcaster using Morphiate or Strangeify.
Wish granting might be a new thing, but I just keep thinking of the Wishing Well from Romantic Garden Stuff... so how that would play out is questionable...
Protection spells could be a new thing and be sort of opposite of the recent "Chased by Death" trait. Or they could be not much different from spending aspiration points from the Rewards Store.
Teleportation wouldn't be unique or new. You can teleport your Sim in just Base Game. You can have your Sim level their wellness skill in Spa Day to teleport. Vampires use Mist Form. Spellcasters can Transportalate. Werewolves can dig tunnels.
Invisibility would certainly be new... but kind of weird since Ghosts don't even go invisible...
So... I don't see a lot of unique in terms of powers... 🤔 and the presentation would likely be very similar to how previous packs have done them if not something as visually lackluster as a Spellcaster using Dedeathify on a Ghost Sim.
Fairies being able to fight other occults would make them pretty OP, wouldn't it? Because none of the other occults can really fight other occults. They can only really fight their own kind due to a man-to-man sort of way. "Oh, you don't have this occult ability/power? I can only fight you on a human Sim level, then. Put up your dukes!" (But man, it would be pretty cool if an occult Sim could fight another occult Sim via their own unique and special abilities.)
The world suggested... It sounds like it would either be as limited as Realm of Magic or at best like how Life & Death is. One world would be livable (your Sim can reside there) but also limited to a degree for the sake of lots and the other one would be limited in it not being a place your Sim can reside in and having very little of the actual world to interact with. The insects and animals would likely be as interactive as bees from Seasons, rodents from My First Pet Stuff, insects from Eco Lifestyle, mini sheep, mini goats, chickens, cows and llamas from Country Living and crows from Life & Death are.
So, new and unique gameplay doesn't sound likely to me. New and beautiful world? Yeah. CAS that can make a Sim look like a Fairy? Yes. (Would their wings even flutter, though?) New build/buy that hopefully has a good take on the magical? Promising. New and unique gameplay? Err... maybe one or two new things?
I feel fairly sure a Fairies pack will come out some day, but I'm not expecting anything particularly new or unique from it. A "perfect platform" for a game with fairies would have to start with the intention of various occults with truly unique and different abilities as well as carefully planned out interactions for various statures, builds and abilities, and lore from the start.